UNIVERSITY  OF  CALIFORNIA. 


QIKT  OF" 


Class 


ENGRAVED    AND    PRINTED   BY 
ROSENOW   COMPANY,  CHICAGO 


The  Stirling  Company 

Manufacturers  of 

Water -Tube  Safety   Boilers   for   Stationary   and    Marine   Use, 

Superheaters,   Bagasse   Furnaces    and    Conveyors, 

Chain   Grate  Stokers,   Steel   Stacks, 

and   Breechings 

General   Offices: 

Trinity  Building,  New  York,  N.  Y.,  U.  S.  A. 

Works :     Barberton,  Ohio 


Sales  Offices: 

Boston,  Mass.       ...  .      .      Delta  Building  Toledo,  Ohio 720  Monroe  Street 

Philadelphia,  Pa Betz  Building  Chicago,  111 Pullman  Building 

Washington,  D.   C Colorado  Building  New  Orleans,  La Hennen  Building 

Pittsburg,  Pa.         ...       Germania  Bank  Building  Atlanta,  Ga Empire  Building 

Cincinnati,  Ohio         .  ...    Ingalls  Building  San  Francisco,  Cal 32  First  Street 

(      Havana,  Cuba      .      .      Royal  Bank  of  Canada  Building 

Johannesburg,  S.  A.  Yokohama,  Japan  Honolulu,  H.  I. 

Herbert  Ainsworth  A.  S.  Hay  Von  Hamm  Young  Co. 

35  Exploration  Buildings  43  B-Yamashita-Cho  Alexander  Young  Building 

Buenos  Ayres,    Argentine   Republic 

La  Cia  de  Fabricantes   Extrangeros,   Ltda. 

302,   Calle  Balcarce,    326 


Pub.  No.  1205 


Stirling 


A    Book    on    Steam    for    Engineers 


Edited  by 
The    Engineering   Staff  of  The   Stirling   Company 


New  York 

The   Stirling   Company 

Trinity   Building 
1905 


Special     Notice 

Realizing  that  it  is  practically  impos- 
sible to  avoid  errors  or  misprints  in 
the  first  edition  of  a  work  of  this  size, 
the  publishers  cordially  invite  those 
who  note  errors  of  any  kind  to  report 
them,  so  that  the  necessary  correc- 
tions may  be  made  in  future  editions 
THE  STIRLING  COMPANY 


Copyright,  1905,  by  The  Stirling  Company 


Table   of  Contents 

PAGE 

The  Stirling-  Water-Tube  Safety  Boiler       .      .  .         .         .  7 

Water-Tube  versus  Fire-Tube  Boilers      ....  35 

Works  of  The  Stirling-  Company 45 

Heat .  47 

Air 55 

Water 57 

Impurities  in  Boiler  Feed  Water           .....  59 

The  Heating  of  Boiler  Feed  Water           ....  67 

Steam 69 

Moisture  in  Steam 79 

Flow  of  Steam  through  Pipes  and  Orifices  ...         .87 

Superheated  Steam  and  the  Stirling  Superheater            .  93 

Combustion 105 

Fuels  for  Steam  Boilers Ill 

Determination  of  Heating  Value  of  Fuels  ....  131 

Fuel  Burning 141 

The  Stirling-Chain  Grate  Stoker 159 

Utilization  of  Waste  Heat 161 

Chimneys  and  Draft      .         .         .         .         .                  .         .  169 

Analysis  of  Flue-Gases     .         .         .         .         .         .      .   .  181 

Steam  Boiler  Efficiency 187 

Horse-Power  Rating  of  Boilers 195 

Rules  for  Conducting  Boiler  Trials 201 

Table  of  Tests  on  Stirling  Boilers 208 

Boilers  for  Mining  Service    .......  209 

Principles  of  Steam  Piping       .         .         .         .         .         .  213 

Boiler  and  Steam  Pipe  Coverings          .....  219 

Boiler  Cleaning 223 

Care  and  Management  of  the  Stirling  Boiler           .         .  229 

Specifications  for  Masonry  in  Stirling  Boiler  Settings   .  233 

Index                        .                  .  239 


135277 


The   Stirling  Water -Tube   Safety   Boiler 


Shortly  after  the  invention  of  the  double- 
acting  steam  engine  by  Watt,  the  develop- 
ment of  the  water-tube  boiler  began,  but  of 
the  many  designs  which  appeared  during  the 
succeeding  half  century  none  proved  success- 
ful. Yet  not  all  of  the  ideas  underlying  these 
early  and  crude  designs  were  valueless,  and 
after  a  long  course  of  experimenting  some 
of  them  were  gradually  worked  out  to  a 
practical  application,  and  the  water-tube 
boiler  then  became  a  commercially  successful 
steam  generator.  It  was  far  from  being 
perfect,  however,  as  many  of  the  most  ad- 
vanced ideas  of  inventors  could  not  be  em- 
bodied in  these  early  types  of  boilers,  because 
of  the  lack  of  suitable  material  to  construct 
the  parts,  and  the  then  inadequate  mechanical 
facilities  for  building  such  boilers.  In  con- 
sequence of  these  manufacturing  limitations, 
the  general  design  narrowed  down  to  some 
arrangement  in  which  steam  was  generated 
in  slightly  inclined  tubes,  and  discharged 
into  one  or  more  upper  drums.  These  parts 
were  all  easily  made  with  the  materials  and 
mechanical  facilities  available  at  that  time. 
One  almost  insuperable  difficulty  remained, 
and  that  was  to  devise  safe  and  efficient  means 
of  providing  passageway  from  the  tube  ends 
into  the  drums.  Out  of  the  hundreds  of 
methods  tried,  but  few  proved  to  be  even 
approximately  successful,  and  there  is  yet 
to  be  found  a  method  which  can  be  considered 
entirely  satisfactory.  In  consequence  of  the 
complexity  of  parts  required  in  these  various 
designs  for  connecting  the  tubes  and  the 
drums,  cast  iron  was  the  only  available 
material,  and  very  unfortunately,  its  use  for 
making  such  parts  became  common. 

The  tendency  to  follow  in  the  beaten  track 
is  well  illustrated  in  this  case,  because  until 
about  two  decades  ago  practically  all  of  the 
various  water-tube  boilers  which  had  achieved 
any  success  were  more  or  less  complicated 
developments  of  the  general  scheme  of  at- 
taching nearly  horizontal  tubes  to  a  drum. 
In  consequence,  all  of  them  were  distinguished 
by  a  multitude  of  joints,  caps,  bolts,  headers, 
water-legs,  nipples,  and  other  objectionable 
features,  while  practically  all  of  them  were 


compelled  to  use  cast  iron  in  headers,  return- 
bends,  and  other  parts  of  complicated  shape 
subjected  to  high  pressure.  As  steam  pres- 
sures and  the  sizes  of  boilers  were  gradually 
increased,  the  defects  of  this  general  design 
were  found  to  be  many,  and  as  each  defect 
developed,  further  complication  was  intro- 
duced to  correct  it. 

These  complications  being  inherent  in  the 
general  design,  it  follows  that  their  elimination 
demanded  the  development  of  a  new  type  of 
boiler  so  essentially  different,  that,  without 
introducing  any  new  defects,  it  would  be 
free  from  those  affecting  the  older  types  whose 
possibilities  of  development  had  been  ex- 
hausted. The  problem  of  producing  such  a 
boiler  received  the  earnest  attention  of  many 
engineers,  yet  there  was,  and  is  now,  but 
one  satisfactory  solution  for  that  problem,  the 
STIRLING  WATER-TUBE  SAFETY  BOILER,  as 
now  manufactured  and  offered  by  THE  STIR- 
LING COMPANY. 

Every  great  invention  is  the  result  of 
gradual  evolution,  and  the  Stirling  boiler 
is  no  exception  to  this  law.  The  first  boilers 
of  this  type  contained  one  mud  drum  and 
only  two  steam  drums.  These  boilers  were 
crudely  constructed,  and  in  their  installation 
but  little  attention  was  paid  to  those  minor 
details  the  aggregate  of  which  constitute 
perfection.  Crude,  however,  as  these  first 
boilers  were,  they  conclusively  demonstrated 
that  the  principle  of  the  boiler  is  correct  and 
that  great  possibilities  lay  in  the  development 
of  its  application.  These  points  having  been 
established,  THE  STIRLING  COMPANY  was 
formed,  the  boiler  was  developed,  and  its 
construction  was  perfected,  but  its  principle 
was  and  always  has  been,  the  same.  In  its 
improved  form,  as  described  in  the  following 
pages,  it  has  met  every  demand,  and  fulfilled 
every  requirement. 

The  Stirling  Boiler  ( Figs,  i  and  2  )  con- 
sists of  three  upper  or  steam  drums,  each 
connected  by  a  number  of  tubes  (called  a 
"bank")  to  a  lower  or  mud  drum.  Suitably 
disposed  firetile  baffles  between  the  banks 
direct  the  gases  into  their  proper  course. 
Shorter  tubes  connect  the  steam  spaces  of  all 


8  THE    STIRLING    WATER-TUBE    SAFETY    BOILER 

upper  drums,  also  water  spaces  of  front  and  plicity   and   eliminates   the   complication   of 

middle  drums.     The  boiler  is  supported  on  the  older  types. 

a  structural  steel  framework,  around  which  The  Drums  vary  from  36  to  54  inches  in 

is  built  a  brick  setting  whose  only  office  is  diameter    and    are    made    of   the    best    open 

to   provide   furnace   space,    and   serve   as   a  hearth  flange  steel.     The  plates  extend  the 


FIG.    1.    THE   STIRLING   WATER-TUBE  SAFETY  BOILER-SECTIONAL  SIDE  ELEVATION 
THE    RED,    YELLOW   AND    BLUE    SECTIONS    RESPECTIVELY    INDICATE-RED    BRICK,    FIRE-BRICK,    AND    CONCRETC 

housing  to  confine  the  heat.  The  entire  entire  distance  between  heads,  hence  there 
front  is  of  metal  of  appropriate  and  artistic  ape*  no  circular  scams.  The  longitudinal 
design.  These  parts,  together  with  the  usual  'seams — which  are  double  or  triple  riveted 
valves  and  fittings,  constitute  the  completed  according  to  the  working  pressure  to  be  car- 
boiler,  which  represents  the  acme  of  sin;-  ried — are  so  placed  that  they  are  not  exposed 


FRONT    ELEVATION    AND    SECTION 


to  high  temperature.  The  drum  heads  are 
hydraulically  dished  to  proper  radius;  each 
drum  is  provided  with  one  manhole,  and  the 
manhole  plate  and  arch  bars  are  of  wrought 
steel;  four  manhole  plates,  which  can  be 


tions  in  them,  as  evidenced  by  the  sectional 
view  shown  in  Fig.  3. 

The  Tubes  are  best  lap- welded  mild  steel. 
They  are  slightly  curved  at  the  ends  to  permit 
them  to  enter  the  drums  normally  and  to 


FIG.  2.      THE   STIRLING   WATER-TUBE   SAFETY   BOILER-SECTIONAL   FRONT   ELEVATION 
THE    RED,    YELLOW    AND    BLUE    SECTIONS    RESPECTIVELY    INDICATE    RED    BRICK,    FIRE-BRICK,    AND    CONCRETE 


removed  in  ten  minutes,  give  access  to  the 
entire  interior  of  the  boiler,  and  expose  every 
tube  end,  rivet,  and  joint.  The  drum  in- 
teriors are  perfectly  clear;  there  are  no  baffles, 
stays,  tie-rods,  mud  pipes,  or  other  obstruc- 


provide  for  free  expansion  of  the  boiler  when 
at  work.  The  tubes  are  expanded  directly 
into  reamed  holes  in  tube  sheets  of  the  drums, 
hence  the  annular  recess  between  tubes  and 
the  cast  headers  of  some  types  of  boiler  is 


10 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


eliminated,  and  failure  of  tubes  by  pitting 
through  corrosion  caused  by  accumulation 
of  soot  in  these  recesses  is  avoided.  There  are 
no  short  nipples  and  no  tube  joints  in  places 
which  can  be  reached  only  by  jointed  handles 
on  the  tube  expander,  rendering  it  impos- 
sible to  determine  when  the  tube  has  been 
properly  expanded.  In  the  Stirling  every 
tube  end  is  visible  and  accessible. 

Steel  Framework — As  the  entire  weight 
of  boiler  and  contents  is  supported  on  the 
steel  framework,  cracking  of  the  setting  due 
to  unequal  settlements  is  obviated,  and  no 
blocking  is  needed  when  the  brickwork  has 
to  be  repaired.  The  design  of  framework 
can  be  modified  to  suit  special  conditions.* 


Furnace — The  design  of  the  Stirling 
furnace  is  a  distinct  advance  over  previous 
practise,  and  offers  advantages  wholly  un- 
obtainable under  some  types  of  boiler,  and 
obtainable  under  the  others  only  by  a  pro- 
hibitive increase  in  floor  space.  Referring 
to  Figs  i  and  2 ,  it  will  be  seen  that  a  fire- 
brick arch  is  sprung  over  the  grates  and  im- 
mediately in  front  of  the  first  bank  of  tubes. 
The  large  trir.ngular  space  between  boiler 
front,  tubes,  and  mud  drum,  is  available  for 
combustion  chamber,  and  for  installation 
of  sufficient  grate  surface  to  meet  the  require- 
ments of  the  lowest  grades  of  fuel,  all  in 
marked  contrast  to  boilers  of  the  internally 
fired  type,  and  many  water-tube  boilers  in 


FIG.   3.     SECTION  THROUGH  STEAM  DRUM,   SHOWING  ABSENCE  OF  BAFFLES  OR  OTHER  COMPLICATIONS 


Brick  Setting — This  is  so  clearly  shown 
by  the  cuts  (  Figs,  i  and  2 )  that  extended 
description  is  unnecessary.  It  is  all  plain, 
straight  work,  which  can  be  done  by  any  good 
brick  mason  who  can  read  lucid  instructions 
and  a  simple  drawing.  No  special  shapes  or 
other  material  not  found  in  open  market  are 
needed.  Any  necessary  repairs  to  brickwork 
can  be  made  without  disturbing  the  boiler 
connections.  The  setting  is  provided  with 
numerous  doors  of  ornamental  design  (  Fig. 
4 ) ,  which  give  access  to  all  parts  for 
cleaning. 


which  only  the  same  grate  surface  is  available 
whether  the  vertical  rows  contain  few  or 
many  tubes. 

Kentf   says:  "Coal  can  be   burned  without 
s:noke,  provided: 

(I)  "The  gases  are  distilled  from  the  coal 
slowly. 

(II)  "That  the    gases   when  distilled  are 
brought  into  intimate  contact  with  very  hot  air. 

(III)  "That  they  are  burned  in  a  hot  1 1  re- 
brick  chamber. 

(IV)  "That   while  burning  they  are  not 
allowed  to  come  into  contact  with  compara- 


*As  an  evidence  of  the  direct  advantages  resulting  from  this  manner  of  supporting  the  boiler.  we 
refer  to  an  explosion  of  natural  gas  in  the  furnace  of  a  Stirling  Boiler  at  the  American  Tin  Plate  Com- 
pany's plant  at  Elwood,  Ind.  Although  the  force  of  the  explosion  \vas  sufficient  entirely  to  demolish 
the  brickwork,  the  boiler  was  uninjured  in  any  way  whatever.  The  brick  was  replaced  and  the  boiler 
put  into  commission,  without  its  having  been  necessary  to  make  any  repairs  whatsoever  to  the 
bciler  proper.  A  recent  similar  explosion  under  a  boiler  fired  with  oil  at  Works  of  Santa  Monica,  (Cal.) 
Brick  &  Tile  Mfg.  Co.  showed  precisely  the  same  result  —  brickwork  completely  demolished,  but  boiler 
uninjured.  ''(Steam  Boiler  Economy,  First  Edition,  p.  156. 


ADVANTAGES   OF   THE    STIRLING  CONSTRUCTION 


11 


tively  cool  surfaces,  such  as  the  shell  or  tubes 
of  a  steam  boiler;  this  means  that  the  gases 
shall  have  sufficient  space  and  time  in  which 
to  burn  before  they  come  into  contact  with 
the  boiler  surfaces." 

The  first  condition  demands  careful  firing, 
and  sufficient  grate  surface ;  this  grate  surface 
is  available  in  the  Stirling  furnace. 


carried  in  stock  by  all  fire-brick  dealers,  in 
contrast  to  the  special  formed  bricks  (ob- 
tainable only  from  the  manufacturer)  re- 
quired by  many  types  of  water- tube  boiler. 
Another  marked  advantage  of  the  Stirling 
baffies  is  that  since  no  tubes  pass  between  or 
through  the  tiles  ( see  Fig.  5  ) ,  they  are  not 
pried  apart  and  made  leaky  by  distorted 


FIG.  4.     CLEANING    DOORS   WITH   ASBESTOS    PACKING  WASHERS 


The  second  requirement  is  preeminently 
met  by  introduction  of  the  brick  arch,  which 
absorbs  heat  from  the  fire,  becomes  an  incan- 
descent radiating  surface  similar  to  roof  of  a 
reverberatory  furnace,  heats  up  any  air  ad- 
mitted over  the  fuel,  and  ignites  by  radiation 
the  gases  distilled  from  the  coal;  it  insures 
an  even  distribution  of  the  gases,  obviates 
their  concentration  at  any  one  point  and 
prevents  the  boiler  from  being  chilled  by 
inrush  of  cold  air  when  the  furnace  doors 
are  opened. 

The  third  requirement  is  met  because  the 
arch  in  combination  with  the  furnace  walls 
forms  a  fire-brick  chamber  of  large  capacity. 

The  fourth  requirement  cannot  be  met  by 
any  internally- fired  boiler,  or  water- tube 
boiler  in  which  tubes  form  the  roof  of  the 
furnace.  In  the  Stirling  furnace  the  gases 
do  not  come  into  contact  with  tubes  until  they 
pass  out  of  the  fire-brick  chamber  under  the 
arch,  and  this  chamber  is  of  sufficient  size  to  al- 
low the  gases  space  and  time  in  which  to  burn. 

Baffles  and  Course  of  Gases — The  baffle 
walls  rest  directly  upon  the  tubes,  and  guide 
the  course  of  the  gases  up  the  front  bank, 
down  the  middle  and  up  the  rear  bank,  thus 
bringing  them  into  such  intimate  contact 
with  the  boiler  surface  that  the  heat  is 
quickly  and  thoroughly  extracted  from  them. 
In  no  other  boiler  are  the  gases  compelled 
to  travel  as  far  before  reaching  the  stack, 
and  the  effect  upon  economy  is  evident.  The 
baffles  are  made  of  plain  rectangular  firetile 


tubes;  they  can  be  removed  and  replaced 
without  disturbing  a  tube.  Baffles  built 
across  the  tubes,  as  in  many  boilers,  are 
damaged  by  pulling  a  faulty  tube  through 
them,  and  can  be  repaired  in  but  one  way — by 
removal  of  every  tube  necessary  to  permit  a 
man  to  crawl  in  and  reach  the  defective  spot. 


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FIG.   5.      ELEVATION    AND    SECTION    OF   FIRETILE   BAFFLES 
IN  STIRLING  BOILERS 

ADVANTAGES  OF  THE   STIRLING 
CONSTRUCTION. 

Such  advantages  as  have  not  already  been 
named  will  now  be  pointed  out.  When  com- 
parisons are  made  with  other  types,  they 
are  given  not  with  the  intention  of  attacking 
or  disparaging  those  types,  but  merely  to 


RAPID    CIRCULATION    OF   WATER 


bring  out  the  superior  points  of  the  Stirling 
water-tube  safety  boiler. 

Simplicity  —  There  are  no  details  of 
complicated  shape;  no  flat  surfaces,  tie-rods, 
water-legs,  headers,  return-bends,  outside 
circulating  pipes  to  plug  up ;  no  multitudinous 
handhole  plates  to  be  removed  and  packed 
with  gaskets,  or  be  ground  and  scraped  to  a 
fit  whenever  boiler  is  opened;  no  baffles  or 
mud  pipes  in  the  drums;  no  short  nipples, 
seams  exposed  to  heat,  or  parts  inaccessible 
for  cleaning. 

Expansion  and  Contraction — In  the 
Stirling  the  mud  drum  is  not  embedded  in 
brickwork,  but  is  suspended  on  the  tubes 
which  connect  it  with  the  upper  drums. 


such  as  caused  when  one  side  of  the  furnace 
is  being  cleaned  and  other  side  is  excessively 
hot,  is  taken  up  by  the  curve  in  the  tube. 
The  boiler  therefore  stays  tight,  and  is 
entirely  free  from  the  stresses  and  frequent 
leaks  caused  by  unequal  expansion  of  straight 
tubes  rigidly  connected  at  each  end  to  headers, 
water-legs,  or  large  drums.*  It  will  thus  be 
seen  that  the  bent  tube  performs  in  the  boiler 
the  same  function  as  an  expansion  loop  in  a 
steam  line,  and  that  its  successful  introduc- 
tion in  the  Stirling  boiler  is  a  distinct  and 
far-reaching  advance  in  steam  engineering. 

Rapid  Circulation — The  path  of  the 
circulation  in  the  Stirling  is  as  follows: — The 
water  is  fed  into  upper  rear  drum,  passes 


FIG.  6.     FORGED   STEEL   DRUM   HEADS  AND   PADS   FOR   WATER   COLUMN   CONNECTIONS 


While  in  many  water-tube  boilers  the  weight 
of  all  the  tubes  and  heavy  headers  must  be 
supported  by  a  single  row  of  nipples  in  front 
and  another  row  at  the  rear  of  the  boiler — 
which  nipples  frequently  work  loose  owing  to 
the  vibrations  ever  present  in  a  boiler  when  at 
work — the  method  of  suspension  in  the 
Stirling  is  radically  different;  here  the  mud 
drum  is  suspended  on  all  the  long  tubes  and 
the  weight  carried  by  each  tube  in  supporting 
the  drum  and  its  contained  water  is  only 
about  forty  pounds.  Besides  this  the  tubes 
are  curved,  so  that  each  one  may  independ- 
ently of  the  others  expand  or  contract 

In  consequence  of  this  construction,  not 
only  may  the  mud  drum  with  perfect  freedom 
move  an  amount  representing  the  resultant 
expansion  of  the  boiler,  but  any  difference 
in  expansion  between  the  individual  tubes, 


down  the  rear  bank  of  tubes  to  the  lower 
drum,  thence  up  the  front  bank  to  forward 
steam  drum.  Here  the  steam  formed  during 
passage  up  the  front  bank  disengages  and 
passes  through  the  upper  row  of  cross  tubes 
into  the  middle  drum,  while  the  solid  water 
passes  through  the  lower  cross  tubes  into 
middle  drum,  then  down  the  middle  bank  to 
lower  drum,  from  which  it  is  again  drawn  up 
the  front  bank  to  retrace  its  former  course 
until  it  is  finally  evaporated.  The  steam 
generated  in  the  rear  bank  passes  through 
cross  tubes  to-the  center  drum. 

The  temperature  of  gases  in  contact  with 
the  tubes  will  evidently  be  greatest  at  the 
bottom  of  the  front  bank,  and  gradually 
decrease  as  the  gases  proceed  along  their 
course  to  the  breeching.  Obviously  then  the 
velocity  of  water  circulation  and  quantity  of 


*For  a  remarkable  illustration  of  the  effects   of  unequal   expansion  of  such  tubes,  see   photograph, 
pp.  546-547,  in  Power,  Sept.  1904. 


IMPOSSIBILITY   OF   FORMING    STEAM    POCKETS 


15 


steam  generated  will  be  a  maximum  in  the 
front  bank;  in  the  rear  bank  there  is  a  slow 
circulation  downward  equal  to  the  quantity 
of  water  evaporated  in  the  other  two  banks. 
The  peculiar  benefits  arising  from  this  action 
will  be  discussed  under  caption  "Handling 
Impure  Feed  Water,"  page  19. 

Rapid  circulation  is  essential  for  the  follow- 
ing reasons: 

(1)  To    keep    all   parts    of   the   boiler    at 
practically  the  same  temperature,  thus  elimi- 
nating severe  stresses  due  to  unequal  expan- 
sion. 

(2)  To  permit  quick  raising  of  steam  and 
rapid   response   to   sudden   demands   on   the 
boiler  capacity. 


the  lower  tubes  which  then  become  over- 
heated, and  buckle  and  leak,  and  finally  burn 
out.  So  inadequate  are  these  nipples  and 
headers  that  recent  experiments  of  M.  Brull 
have  shown  that  in  boilers  whose  circulation 
is  constricted  by  nipples  or  narrow  water- 
legs,  the  circulation  in  the  upper  tubes 
reverses,  that  is,  it  goes  from  the  front  to  rear 
instead  of  in  the  opposite  way  as  intended.* 
In  consequence  of  this,  much  matter  sus- 
pended in  the  water  is  swept  into  the  bottom 
tubes,  which  fact,  in  connection  with  the 
steam  pockets,  explains  why  those  tubes  so- 
rapidly  fail. 

In  the  Stirling  boiler  there  is  no  constriction 
of   the   circulation,    as   each   tube   discharges 


DRUM    LUG  MANHOLE  AND  ARCH    BARS  STEAM    NOZZLE   PAD 

FIG.  7.     FORGED   STEEL   DETAILS   OF  THE   STIRLING    BOILER 


(3)  To  sweep  away  from  the  heating 
surfaces  all  steam  bubbles  as  fast  as  formed, 
and  thereby  prevent  "steam  pockets"  which 
quickly  burn  out  the  tubes.  This  is  so  par- 
ticularly the  case  where  intense  local  heating 
occurs  due  to  use  of  gas  or  oil  fuel,  that  some 
types  of  boiler  fairly  well  adapted  to  coal 
cannot  be  successfully  used  with  these  fuels. 

The  third  requirement  is  met  only  indif- 
ferently or  not  at  all  in  those  types  of  boilers 
in  which  tubes  often  numbering  as  many  as 
eighteen,  must  discharge  their  entire  content 
of  steam  and  water  through  a  narrow  water- 
leg,  or  worse  still,  through  a  single  nipple 
whose  cross  section  is  equal  to  that  of  but  one 
tube.  At  150  pounds  gauge  one  cubic  foot 
of  water,  when  converted  into  steam,  will 
have  a  volume  of  about  151  cubic  feet.  In 
consequence  of  this  great  increase  in  volume,  as 
soon  as  the  boiler  is  forced  the  nipple  area 
becomes  insufficient,  steam  pockets  form  in 


directly  into  the  drums,  without  intervention 
of  headers,  nipples  or  water-legs.  The  nearly 
vertical  position  of  the  tubes  also  promotes 
rapid  circulation,  hence  steam  pockets  cannot 
form,  and  a  fruitful  cause  of  interrupted 
service  and  tube  renewals  in  other  types  is 
thus  eliminated  from  the  Stirling.  The 
record  of  this  boiler  affords  incontestable 
evidence  on  this  point.  To  cite  a  case:  In 
a  plant  using  Stirling  boilers  in  connection 
with  water-power,  the  water-wheels  failed 
and  required  several  days  for  repairing.  As 
the  service  could  not  be  interrupted  the  only 
recourse  was  to  operate  the  boilers  continu- 
ously at  over  100  per  cent,  above  rating  until 
the  wheels  could  be  repaired.  Considerable 
damage  to  the  boiler  was  expected  as  a 
matter  of  course.  When  the  run  was  over  it 
was  found  that  the  furnace  lining  had  been 
melted  down  f  and  must  be  renewed,  but  no- 
damage  of  any  kind  to  the  boilers — not  even 


*Cf.  "Appareil   pour   1'dtude    de    la   circulation    dans    les    chaudieres  a  tubes  d'eau,  par  M.    Brull," 
Comptes  Rendus  de  la  Societe  de  I  Industrie  Minerale.     Nov. -Dec.,  1901.         fOil  fuel  was  used. 


BOILER    EXPLOSIONS    DUE    TO    CAST    IRON 


17 


a  leaky  tube — was  noted,  and  not  one  penny 
was  expended  for  repairing  the  boiler  itself. 

Safety — From  the  foregoing  it  is  evident 
that  the  Stirling  is  preeminently  a  safety 
boiler.  Since  all  parts  are  of  wrought  metal 
and  either  cylindrical  or  spherical  in  form, 
so  that  their  strength  can  be  accurately  com- 
puted, and  all  flat  surfaces,  stay-bolts  and 
braces  have  been  discarded,  all  tendency 


too  frequently  allow  small  differences  in  first 
cost  to  lead  to  the  purchase  of  boilers  inhe- 
rently weak  and  dangerous. 

All  serious  explosions  result  from  the  sud- 
den liberation  of  the  energy  contained  in 
large  masses  of  steam  and  water.  If  a 
rupture  occurs  in  the  shell  of  a  tubular, 
flue,  or  cylindrical  boiler,  the  energy  of  all 
the  steam  and  water  within  is  suddenly 


FIG.  8.     STEEL   FIRING   AND  ASH-PIT   DOORS   OF  THE   STIRLING   BOILER 


to  distortion  under  pressure  is  avoided. 
The  design  once  and  forever  eliminates 
from  boiler  construction  any  necessity  for 
that  most  treacherous  material  and  fruitful 
source  of  ruptures  in  other  types — 
cast  iron — whether  confessedly  such,  or 
disguised  under  such  trade  names  as  "semi- 
steel,"  "composition,"  "  flowed- steel,  " 
"malleable  metal,"  etc.  In  many  countries 
the  use  of  cast  metal  is  forbidden  by  law. 
Purchasers  too  often  fail  to  realize  the 
enormous  power  contained  in  steam  and 
water  at  a  high  temperature  under  pressure, 
and  that  the  energy  stored  in  boilers  is 
sufficient  to  throw  them  straight  upward  a 
height  of  from  one  to  four  miles,  and  they 


released,  to  the  destruction  of  the  boiler 
itself,  and  frequently  of  its  surroundings, 
with  accompanying  loss  of  life  The  same 
disastrous  consequences  attend  a  rupture 
in  a  water-tube  boiler  when  the  part  giving 
away  contains  a  large  quantity  of  steam 
and  water  Thus,  the  bursting  of  headers 
in  the  horizontal  type  of  water-tube  boilers 
is  frequently  accompanied  by  the  most 
destructive  results,  owing  to  the  fact  that, 
although  they  do  not  in  themselves  contain 
large  volumes  of  water,  they  are  connected 
with  a  number  of  tubes,  which  in  the  ag- 
gregate, contain  a  very  large  quantity  of 
water  and  steam;  and  when  the  cast  iron 
gives  away,  the  rupture  is  not  confined  to 


HANDLING    IMPURE    FEED    WATER 


19 


a  single  spot,  but  extends  throughout  the 
entire  section  of  the  header,  thus  instantly 
liberating  the  water  and  steam  contained 
in  all  the  tubes  expanded  into  it.  A  rupture 
in  cast  iron  must,  of  necessity,  extend 
throughout  its  entire  length  or  breadth; 
while  a  rupture  in  wrought  iron,  or  soft 
steel,  is  local,  and  can  be  enlarged  only 
by  the  continued  application  of  force.  None 
of  the  so-called  "safety  boilers"  then,  in 
which  cast  metal  is  used,  are  worthy  of  the 
name.  The  term  can  be  applied  only  to 
boilers  in  which  all  possible  points  of  rupture 


has  been  so  reduced  that  baking  of  the 
scale  to  a  flinty  hardness  is  obviated,  hence 
the  deposit  is  soft  and  easily  removed  unless 
neglected  for  long  periods  of  time.  Even 
in  this  case  the  tube  cannot  be  burned  be- 
cause of  the  low  -  temperature  of  the  gases 
surrounding  it. 

Hence,  before  passing  into  the  front 
bank  the  water  is  purified,*  and  the  dan- 
ger of  scale  formation  in  the  parts  of 
the  boiler  that  are  subjected  to  the  highest 
temperature  is  greatly  reduced;  consequently 
the  interior  of  these  tubes  remains  clean, 


FIG.  9.    WATER  COLUMN  AND  CONNECTIONS,  WITH   QUICK-CLOSING   GAUGE   GLASS   FITTINGS 


are  confined  to  portions  such  as  the  tubes, 
containing  small  masses  of  water,  and  which 
are  constructed  of  a  material  in  which 
such  rupture  will  remain  local.  This  con- 
dition is  admirably  fulfilled  in  the  Stirling 
water-tube  safety  boiler. 

Handling  Impure  Feed  Water — In  the 
course  of  the  feed  water  from  the  feed  drum 
to  mud  drum  any  precipitate  formed  under 
influence  of  the  temperature  and  pressure 
must  drop  into  the  mud  drum,  which  is 
protected  from  intense  heat  of  the  furnace, 
and  acts  as  an  excellent  settling  chamber. 
The  scale-forming  matter  which  crystallizes 
out  under  action  of  the  temperature  and 
pressure  will  deposit  on  the  rear  bank  of 
tubes,  but  since  the  gases  have  passed  two 
banks  of  tubes  before  reaching  those  where 
the  deposit  is  formed,  their  temperature 


and  heat  is  transmitted  more  rapidly  to 
the  water,  thus  not  only  preventing  the 
tubes  from  becoming  overheated  and  burned 
out,  but  at  the  same  time  maintaining 
the  efficiency  of  the  boiler  If  there  are 
impurities  in  the  feed  water  they  must  be 
deposited  somewhere  in  the  boiler,  hence  the 
only  recourse  is  to  devise  means  to  deposit 
them  where  they  will  do  the  least  harm. 
This  is  accomplished  by  settling  the  precip- 
itates where  they  can  be  blown  off  without 
gathering  on  the  heating  surface,  and  by 
causing  the  scale  to  form  on  the  coolest 
heating  surface  where  it  will  affect  the 
economy  the  least,  and  remain  so  soft  that 
its  removal  is  easy.  All  this  is  accomplished 
to  greater  degree  in  the  Stirling  than  in  any 
other  boiler,  and  in  many  types  it  is  not 
accomplished  at  all.  For  example,  in  hor- 


*This  explains  why  the  water  spaces  in  rear  and  middle  drum  are  not  connected.  By  compelling 
all  the  water  to  traverse  the  rear  bank  it  is  purified  before  reaching  the  parts  of  the  boiler  exposed  to 
the  highest  temperatures. 


CLEANING    THE    INTERIOR    OF   THE    BOILER 


21 


izontal  water-tube  boilersf  the  water  is 
fed  into  upper  drums,  flows  to  the  rear, 
then  down  the  nipples  to  rear  header  (or 
water-leg),  then  into  the  tubes.  Owing 
to  the  constricted  area  of  nipple  and  header 
the  velocity  of  water  is  multiplied  in  pro- 
portion to  the  number  of  tubes  connected 
to  one  header.  As  the  capacity  of  water 
to  convey  solids  varies  with  the  sixth  power 
of  the  velocity,!  only  a  small  portion  of 
the  precipitates  formed  drops  directly  into 
the  mud  drum,  while  the  balance  is  swept 
into  the  tubes.  As  the  lower  tube  is  the 
hottest,  it  draws  in  the  greatest  quantity 
of  water,  hence  forms  the  greatest  quantity 
of  scale,  to  which  is  added  the  precipitate 
drawn  in  with  the  water.  In  consequence 
the  deposit  on  the  tubes  is  the  sum  of  the 
scale  and  the  precipitate.  The  most  vital 
point,  however,  is  that  this  deposit  forms 
in  greatest  quantity  in  the  hottest  tubes  and 
burns  to  a  flinty  hardness,  consequently  its 
removal  is  tedious  and  costly.  Owing  to  the 
great  heat  on  the  bottom  tubes,  a  small  de- 
posit will  invariably  cause  the  tube  to  burn, 
bag,  or  crack. 

A  most  fruitful  cause  of  burnt  tubes  is  a 
piece  of  scale  which  becomes  detached  and 
falls  on  the  bottom  of  the  tube,  and  the  spot 
under  it  is  certain  to  burn  out  quickly  The 
Stirling  is  free  from  this  source  of  tube  de- 
struction, because  while  the  scale  will  not 
form  in  the  hotter  tubes  unless  the  boiler  is 
neglected,  even  if  it  does  form  owing  to  such 
neglect  and  a  piece  becomes  detached  it  will 
slide  down  to  the  mud  drum  instead  of  lodging. 

Cleaning  the  Interior — By  removing 
four  manhole  plates,  which  can  be  done  in  ten 
minutes,  the  entire  boiler  interior  is  acces- 
sible for  cleaning.  From  the  preceding 
discussion  it  is  evident  that  the  precipitates 
are  settled  into  the  mud  drum,  whence  they 
are  blown  off  at  intervals ;,  the  scale  is  prac- 
tically confined  to  the  rear  bank  of  tubes,  and 
by  reason  of  escaping  the  high  temperatures 
it  is  soft  and  easily  detached.  Consequently 
it  happens  in  most  cases  that  only  the  rear 
bank  needs  cleaning  each  time  the  boiler 
is  opened,  while  the  others  need  only  occa- 
sional attention.  The  scale  is  quickly  and 
cheaply  removed  by  a  "turbine  cleaner" 


consisting  of  a  cutting  tool  driven  by  a 
water  turbine  attached  to  a  hose,  whose 
operation  requires  no  labor  beyond  that 
necessary  to  guide  the  hose  and  cleaner 
attached,  and  shift  it  from  one  tube  to  an- 
other. Fig.  45*  illustrates  one  of  many 
designs  of  turbine  cleaner  on  the  market. 
So  much  progress  has  been  made  in  the 
development  of  tube  cleaners  that  the  re- 
moval of  scale  from  tubes  (no  matter  whether 
they  be  straight  or  curved,  or  whether  the 
scale  be  heavy  or  light),  is  merely  a  question 
of  the  selection  of  the  tool  or  device  best 
adapted  to  the  work  to  be  done.  The 
matter  is  further  discussed  in  the  chapter  on 
Boiler  Cleaning,  page  223. 

An  objection  occasionally  urged  against 
curved  tubes  by  those  who  have  neither  had 
experience  with  them  nor  investigated  their 
great  advantage  is  that  they  are  difficult 
to  clean,  and  cannot  be  looked  through. 
Neither  objection  has  weight.  The  turbine 
cleaner  traverses  a  straight  or  curved  tube 
with  equal  facility  If  it  did  not,  it  would 
be  impossible  to  clean  some  boilers  whose 
tubes,  though  originally  straight,  distort 
in  service  an  amount  often  exceeding  the 
curves  in  the  Stirling  tubes. 

The  thickness  of  scale  in  a  tube  cannot  be 
judged  by  looking  through  the  tube,  because 
if  the  scale  has  evenly  formed  around  the 
tube  a  difference  of  three-eighths  of  an  inch 
in  the  bore  cannot  be  detected  by  the  eye 
at  a  point  six  feet  away  Where  the  in- 
crustation is  heaviest  on  the  bottom,  due  to 
deposit  of  precipitate  and  scale,  as  common 
in  all  horizontal  water-tubes,  the  departure 
from  the  round  bore  can  be  seen,  and  this 
fact  doubtless  lead  to  the  belief  that  abil- 
ity to  see  through  a  tube  is  an  advantage. 
The  actual  fact  is  that  the  only  way  to  know 
that  there  is  no  deposit  on  a  tube  is  to  pass 
through  it  a  turbine  tube  cleaner,  or  a  ball  of 
proper  size  attached  to  a  cord,  and  this  test 
applies  equally  well  to  all  tubes  whether 
straight  or  curved. 

Every  inch  of  surface  in  the  Stirling  boiler 
can  be  reached  and  cleaned,  and  the  time 
required  for  opening,  cleaning,  closing  and 
steaming  up  the  boiler  is  often  considerably 
less  than  that  required  merely  to  remove 


fAttempts  have  been  made,  but  without  success,  to  provide  horizontal  boilers  with  an  equivalent 
of  the  Stirling  mud  drum,     One  such  design  is  shown  in  Power,  p.  565,  Sept.,  1904.     *Page  225. 
JIf  the  velocity  is  tripled  the  carrying  capacity  is  729  times  as  great,  etc. 


DURABILITY   AND    FREEDOM    FROM    REPAIRS 


23 


and  refit  the  caps  over  tube  ends  in  other 
types  of  boiler. 

Cleaning  the  Exterior — Ample  cleaning 
doors  are  provided  both  in  the  sides  and  rear 
of  the  setting,  so  that  the  exterior  of  the 
heating  surfaces  may  be  kept  clean  and  all 
accumulations  of  soot,  ashes,  etc.,  blown 
off  as  rapidly  as  they  form  by  using  a  steam 
blower-pipe  which  is  furnished  with  every 
boiler.* 

The    tubes    being    only    slightly    inclined 


of  irregular  shape  and  uncertain  strength; 
stresses  due  to  unequal  expansion;  multi- 
tudes of  caps,  joints  and  nipples,  and  simi- 
lar objectionable  details,  the  Stirling  boiler 
is  free  from  parts  liable  to  get  out  of  order. 
The  prevention  of  scale  deposits  in  the  hottest 
tubes;  the  perfect  facilities  for  keeping  the 
boiler  clean;  the  rapidity  of  water  circula- 
tion and  impossibility  of  forming  steam 
pockets,  all  combine  to  protect  the  tubes 
against  burning  out.  Hence  the  necessity 


FIG.  10.     IRON   DOOR  AND   FRAME   IN  WALL  OPENING   OPPOSITE   MUD   DRUM 


from  the  vertical,  there  is  no  opportunity 
for  soot  and  dust  to  settle  on  one  side  or  on 
top  of  the  tubes  as  in  boilers  of  the  hori- 
zontal type.  Furthermore,  the  tubes  are 
in  parallel  rows  (not  staggered  as  in  some 
other  types)  and  so  arranged  that  it  is  pos- 
sible to  pass  the  hand,  and  indeed,  the  whole 
arm,  between  two  rows  of  tubes,  and  reach 
those  in  the  last  tier.  The  exterior  surfaces, 
then,  may  with  ease  be  thoroughly  cleaned 
of  soot  and  kindred  deposits. 

Durability — By  reason  of  the  elimination 
of  thick  plates  and  riveted  joints  exposed 
to  the  fire;  cast  metal  of  all  kinds;  parts 


of  repairs  to  the  boiler  itself  is  extremely 
remote.  The  setting  is  simple  and  substan- 
tial and  not  subject  to  derangement  other 
than  the  natural  wear  of  furnace  lining. 

In  consequence  the  Stirling  has  earned  an 
enviable  reputation  for  durability  and  light 
cost  of  repairs.  That  this  reputation  is 
merited  is  evidenced  by  fact  that  according 
to  statistics  recently  received  from  a  plant 
operated  by  careful  and  intelligent  engineers 
the  records  show  that  on  basis  of  equal 
horse-power  hours  the  tube  renewals  in  the 
Stirling  as  compared  with  those  on  a  promi- 
nent type  of  horizontal  water-tube  boiler 


*The  importance  of  being  able  to  clean  a  boiler  thoroughly,  outside  as  well  as  inside  ,and  of  keeping  it 
clean,  was  well  demonstrated  by  a  comparative  test  made  by  one  of  our  engineers  some  time  ago  on  a 
boiler  which  had  been  allowed  to  run  some  months  without  cleaning,  and  accumulate  a  thickness  of 
one-eighth  inch  of  soot  on  the  tubes.  Before  cleaning  the  evaporation  was  found  to  be  8.04  pounds  of 
water  per  pound  of  coal;  and  after  cleaning  the  evaporation  per  pound  of  coal  was  10.30,  a  gain  of  about 
28  per  cent. 


STEAM    AND    WATER    SPACE 


25 


of  steel  header  construction  were  in  ratio  of 
i  to  61,  the  relative  maintenance  account 
in  other  respects  was  as  i  to  3,  and  the  labor 
of  cleaning  6  to  35,  all  in  favor  of  the  Stir- 
ling.* 

Facility  for  Making  Repairs — Practically 
the  only  repairs  needed  to  the  Stirling  boiler 
will  be  tube  renewals,  and  unless  the  boiler 
is  grossly  neglected  such  renewals  will  be 


FIG.  11.     PHOTOGRAPHS  SHOWING  DISTENTION  OF  TUBES 
AT  POINT  OF  RUPTURE 

needed  only  after  many  years,  as  evidenced 
by  fact  that  Stirling  boilers  have  been  in 
service  for  eight  years,  using  hard  coal, 
bituminous  coal,  natural  and  forced  draft 
and  oil  fuel,  without  losing  a  tube  or  even 
developing  a  leak.  Should  tube  renewals 
become  necessary  they  are  quickly  and 
easily  made. 

All  tube  failures  reduce  to  four  classes: 
(T)     Pitting,    which    causes    pin    holes    to 
be  formed. 

(2)  Defective  welds,  which  cause  the  tube 
to  open  as  in  A,  Fig    n. 

(3)  An     initial    bagging    resulting     in     a 
rupture,  as  in  B. 

(4)  Scabbing    and    blistering    as    in    C. 
In  the  first  case,  the  tube  is  not  enlarged, 

and  may  be  drawn  through  a  tube  sheet, 
without  disturbing  other  tubes,  though 
usually  with  difficulty  owing  to  deposits  on 
the  outer  surface. 


In  the  other  cases,  the  tubes  become 
larger  than  their  original  size,  hence  they 
cannot  be  drawn  through  the  tube  sheet, 
water-leg  or  header,  unless  they  are  split 
and  collapsed  inch  by  inch  for  their  entire 
length  beyond  the  point  of  failure,  and  if 
they  also  pass  through  cross  baffles  the  en- 
largement will  pull  out  the  bricks  and  de- 
stroy the  baffle.  To  remove  a  tube  in  this 
way  "is  the  work  of  days,  and  in  consequence 
the  actual  method  used  is  to  cut  out  all 
tubes — numbering  at  times  half  a  dozen 
below  the  defective  one — and  to  avoid  de- 
stroying the  baffles  these  tubes  are  cut  into 
several  pieces. 

In  the  vertical  types  of  water-tube  boiler 
more  recently  introduced  the  tubes  are 
crowded  together  so  closely  that  not  only  is 
it  necessary  to  cut  out  every  tube  in  front 
of  the  defective  one — numbering  at  times 
nearly  a  dozen — but  the  brickwork  must 
be  removed  to  gain  access  to  the  tubes 

Removal  of  tubes  from  the  Stirling  is  ex- 
tremely simple.  As  the  boiler  is  now  con- 
structed the  tubes  are  spaced  as  in  Fig.  1 2 , 
and  each  alternate  space  is  one-half  inch 
wider  than  the  tube  diameter;  to  remove 
an  inner  tube  it  is  merely  necessary  to  cut 
the  tube  as  near  the  tube-sheet  as  possible, 
pass  it  out  through  the  wide  space  between 
the  tubes,  as  indicated  by  the  arrows  in  Fig. 
12,  and  then  remove  it  from  the  setting 
through  either  the  side  or  front  doors  pro- 
vided for  that  purpose.  Consequently,  any 
tube  in  the  Stirling  boiler  as  now  constructed 
may  be  replaced  without  either  disturbing 
any  other  tube,  distorting  the  tube  sheet,  or 
damaging  the  firetile  baffles. 


FIG.    12.     TUBE  SPACING  IN  STIRLING  BOILERS 

Steam  and  Water  Space — Unless  pro- 
vided with  sufficient  steam  and  water  space, 
a  boiler  will  be  subject  to  sudden  fluctuations 
of  pressure;  the  water  level  will  be  unsteady, 


*Also  see  Table  i,  page  33,  referring  to  boilers  at  World's  Columbian  Exposition. 


OPERATION  AT  HIGH  AND  LOW  RATES  OF  EVAPORATION 


27 


and  the  steam  will  frequently  be  wet.  Some 
prominent  types  of  water-tube  boiler  use 
but  one  drum  for  from  four  to  nine  sections 
of  tubes,  but  two  drums  from  ten  to  sixteen 
sections,  and  three  drums  from  eighteen 
to  twenty-one  sections.  Hence  for  their 
entire  range  there  are  but  three  drum  com- 
binations, and  the  steam  and  water  space 
varies  not  with  the  boiler  horse-power  but 
in  wide  jumps  between  combinations.  In 
the  vertical  water-tube  boilers  there  is 
usually  for  all  sizes  but  one  top  drum  of  very 
limited  steam  and  water  capacity. 

In  the  Stirling  boiler  there  are  three  upper 
drums,  which  afford  large  steam  and  water 
spaces,  and  these  vary  strictly  with  the 
boiler  horse-power,  since  increased  capacity 
is  gained,  not  by  stacking  up  tubes  in  suc- 
cessive horizontal  layers  without  increase 
of  drum  capacity,  but  by  adding  sections 
of  tubes  to  the  boiler  width,  and  increasing 
the  drum  lengths  in  proportion 

Dry  Steam — The  production  of  dry  steam 
requires  large  disengaging  surface;  while 
in  many  types  of  boiler  the  effective  disen- 
gaging surface  is  only  a  narrow  strip  over 
the  nipples  and  water-legs  (which  explains 
why  such  boilers  have  to  be  provided  with 
internal  baffles  of  various  kinds,*)  in  the 
Stirling  the  entire  water  surface  of  the 
three  upper  drums  is  available  as  disengaging 
surface,  hence  the  steam  does  not  disturb 
the  water  surface,  and  is  dry.  As  there  is 
no  constriction  of  the  water  circulation, 
and  as  the  middle  drum  from  which  the 
steam  is  drawn  is  somewhat  higher  than 
the  other  two  drums,  and  the  circulation 
of  the  water  in  this  drum  is  downward, 
there  is  absolutely  no  spurting  or  geyser- 
like  action  of  the  water  in  this  drum.  The 
steam  from  the  front  and  rear  drum  must 
also  pass  through  hot  circulating  tubes  which 
dry  it  before  it  reaches  the  central  drum. 

Adaptation  to  Different  Kinds  of  Fuel 
—The  large  space  available  for  furnace  under 
the  Stirling  enables  the  grates  to  be  pro- 
portioned for  coal  of  the  cheapest  grade. 
By  proper  reduction  of  this  grate  surface, 
the  requirements  for  better  grades  of  coal 
can  be  exactly  met.  Should  it  be  desired 
to  burn  wood,  the  most  perfect  form  of 
wood  furnace  can  be  got  simply  by  lowering 


the  grates  to  level  of  firing  floor.  For  burn- 
ing oil  or  gas,  the  only  change  needed  from 
the  standard  furnace  is  to  cover  the  grates 
with  fire-brick  so  disposed  as  to  admit  the 
requisite  quantity  of  air,  and  to  provide 
at  rear  end  of  the  grates  a  loose  checkerwork 
wall  of  fire-brick  against  which  the  heat 
will  impinge.  Should  it  be  necessary  to 
change  from  oil  or  gas  to  other  fuel,  the 
Stirling  furnace  in  an  hour  after  shutting 
off  the  burners  can  be  made  ready  for  firing 
with  coal,  shavings  or  sawdust.  For  burning 
bagasse  it  is  necessary  only  to  provide 
proper  feeding  apparatus  and  suitable  grates, 
and  the  furnace  thus  equipped  may  with 
equal  success  be  used  for  other  fuels.  Con- 
sequently, with  but  trifling  changes  the 
Stirling  furnace  can  be  adapted  to  any  kind 
of  fuel,  and  in  no  case  will  there  be  any 
essential  departure  from  the  general  design, 
or  removal  of  the  arch  which  forms  the  fire- 
brick chamber  necessary  for  a  perfect  furnace. 

The  Stirling  furnace  is  also  well  adapted 
to  installation  of  any  of  the  various  stokers 
in  use,  and  to  such  modifications  as  are  de- 
sirable when  the  boilers  are  installed  in  con- 
nection with  coke  ovens,  heating  furnaces, 
reverberatories  for  copper  smelting,  and 
other  cases  where  the  boilers  are  fired  either 
wholly  by  waste  gases,  or  partly  by  waste 
gases,  and  partly  by  hand. 

Possibility  of  Driving  at  both  Low  and 
High  Rates  of  Evaporation  without  Great 
Loss  of  Fuel  Economy — This  is  a  point  of  the 
highest  importance  in  plants  where  peak  loads 
occur.  To  install  boiler  capacity  sufficient 
to  handle  the  peak  at  regular  rate  of  evapo- 
ration would  require  large  initial  cost,  hence 
the  usual  procedure  is  to  work  the  boilers 
above  rating  during  the  busy  hours  Unless 
the  boiler  can  respond  without  material 
decrease  in  economy  at  the  increased  rate 
of  working  there  will  be  large  wastes  of 
fuel. 

The  Stirling  boiler  meets  this  require- 
ment to  a  degree  not  attainable  with  other 
types,  because  of  its  free  circulation  and 
the  action  of  the  rear  bank  of  tubes.  Here 
the  gases  come  into  contact  with  those  parts 
of  the  boiler  which  receive  the  feed-water, 
hence  the  temperature  difference  between 
gases  and  water  is  a  maximum,  and  the  heat 


*See  "A  bad  case  of  discharge  of  water  with  steam  from  water-tube  boilers."     Vol.  XXVI,   Transac- 
tions American  Society  of  Mechanical  Engineers. 


FUEL    EFFICIENCY 


29 


is  quickly  abstracted  from  the  gases.  The 
economy  therefore  decreases  very  slowly 
as  the  rate  of  driving  is  increased,  and  this 
is  evidenced  by  recent  tests  in  which  a  Stir- 
ling boiler  when  driven  at  rates  of  60  and 
100  per  cent,  above  rating,  showed  diminu- 
tion in  economy  of  but  5.11  and  7.66  per 
cent.,  respectively,  below  the  efficiency  at 
rating. 

Adaptation  to  Hot=Water  Heating — A 
unique  illustration  of  the  advantage  result- 
ing from  the  absence  of  all  constriction  in 
the  path  of  circulation  in  the  Stirling  boiler 
is  afforded  by  the  extensive  use  of  this  boiler 
in  hot-water  heating  plants.  For  such  work 
a  free  passage  of  the  water  in  its  course 
through  the  boiler  is  absolutely  essential. 
This  requirement  is  perfectly  met  in  the 
Stirling,  and  the  same  boiler,  according  to 
the  necessities  of  the  plant,  is  used  to  generate 
steam  at  one  time,  and  at  other  times  to  heat 
water  which  is  pumped  through  the  hot- 
water  mains. 

Space  Occupied — The  Stirling  design  is 
so  flexible  that  the  boiler  can  be  and  is  built 
to  meet  the  varying  requirements  of  height, 
width  and  depth,  so  that  a  200  horse-power 
boiler  can  be  built  to  occupy  from  12  to  22 
feet  in  height,  8  to  15  feet  in  width,  and  14 
to  17  feet  in  depth.  It  is  therefore  equally 
well  adapted  to  boiler-rooms  having  low 
ceilings  and  ample  width,  as  well  as  to  those 
having  little  width  and  ample  height.  More 
horse-power  of  the  Stirling  type  can  be  in- 
stalled in  a  given  number  of  cubic  feet  than 
of  any  other  type  on  the  market. 

BOILER   EFFICIENCY 

Of  all  the  terms  relating  to  boiler  perform- 
ance, none  is  so  much  talked  of,  yet  so  im- 
perfectly understood  and  erroneously  applied 
as  the  word  efficiency.  It  is  therefore  neces- 
sary that  the  different  meanings  of  this 
word  be  clearly  understood. 

"Fuel  Efficiency"  is  the  ratio  between  the 
heat  absorbed  by  the  boiler  and  the  heat 
value  of  the  fuel  burned.  In  nearly  all 
cases  where  the  term  boiler  efficiency  occurs 
it  is  used  in  this  sense,  yet  this  efficiency 
is  quite  secondary  in  importance  to  another 
which  is  thus  defined:  "The  'Commercial 
Efficiency,'  or  the  'Efficiency  of  Capital' 

*Thurston,  "The  Steam  Boiler,"  page  475. 


employed  in  the  maintenance  of  steam 
generating  apparatus  of  a  given  power,  is 
measured  by  the  ratio  of  quantity  of  steam 
produced  to  the  total  cost  of  its  continuous 
production.  This  efficiency  is  a  maximum 
when  that  cost  is  a  minimum."*  Accordingly, 
the  Stirling  boiler  will  be  considered  with  re- 
spect to  both  of  the  above  named  efficiencies. 

Fuel  Efficiency — The  boiler  can  only  ab- 
sorb heat,  but  the  production  of  that  heat 
depends  upon  the  furnace,  consequently  the 
fuel  efficiency  is  not  properly  boiler  efficiency, 
but  efficiency  of  the  combination  of  boiler 
and  furnace.  A  deficiency  in  either  of  these 
will  affect  the  efficiency  of  the  combination. 

The  preceding  discussion  has  set  forth 
the  capabilities  of  the  Stirling  furnace  to 
handle  each  and  any  kind  of  fuel  in  use, 
and  to  insure  complete  combustion  of  the 
gases  distilled  from  fuels  containing  high 
percentages  of  volatile  matter,  and  to  prevent 
extinguishment  of  the  flame  by  contact 
with  cool  boiler  surfaces  over  the  fire.  The 
Stirling  furnace,  therefore,  leaves  nothing 
to  be  desired,  and  its  efficient  performance 
is  merely  a  matter  of  proper  attention  from 
the  fireman. 

In  regard  to  the  Stirling  boiler  proper,  it 
has  already  been  shown:  that  the  surfaces 
between  the  heat  and  water  are  thin,  hence 
absort}  the  heat  quickly;  that  the  circulation 
is  extremely  rapid,  so  that  the  steam  as 
fast  as  formed  is  carried  away,  and  the 
heating  surface  kept  covered  with  water; 
that  the  scale  is  formed  on  the  coolest  sur- 
faces where  it  affects  the  economy  the  least, 
and  that  its  removal  is  so  easy  that  every 
inch  of  surface  of  the  boiler  can  be  kept 
clean  and  efficient;  that  the  course  of  the 
gases  in  contact  with  the  tube  surface  is 
longer  than  in  other  types  of  boiler,  so  that 
the  heat  is  thoroughly  abstracted;  that  in 
the  rear  bank  of  tubes  the  coldest  water 
comes  in  where  the  coldest  gases  go  out, 
hence  the  flow  of  water  and  gas  is  in  opposite 
directions  in  conformity  with  Rankine's 
law  of  economy;  that  leaky  cross-baffles 
have  been  eliminated,  hence  there  can  be 
no  short-circuiting  of  the  gases  to  the  stack; 
that  the  setting  is  simple  and  tight,  hence 
air  leakages  are  obviated;  and  that  there 
are  no  exposed  surfaces  to  cause  loss  by 
condensation. 


SHERRY   BUILDING,    NEW  YORK,    OPERATING    775   H.  P.  OF   STIRLING    BOILERS 

3° 


COMPARISON   OF   TIME    REQUIRED    FOR   CLEANING 


31 


In  consequence  of  these  features,  the 
Stirling  boiler  develops  a  fuel  efficiency  as 
high  as  ever  attained  under  any  type  of 
boiler,  and  with  reasonable  care  its  efficiency 
will  continue  unimpaired  with  use. 

In  practically  every  case  where  efficiency 
tests  are  exhibited,  they  were  made  on 
boilers  which  were  thoroughly  cleaned  and 
handled  by  an  expert.  That  efficiencies  thus 
obtained  do  not  represent  results  obtainable 
in  daily  work  will  be  evident  upon  consider- 
ing that  the  moment  a  boiler  begins  a  run, 
its  surface  acumulates  incrustation  from 
the  water.  In  the  preceding  part  of  this 
article  it  has  been  clearly  shown  that  in 
many  types  of  boiler  the  deposits  form  on 
the  hottest  tubes,  where  beside  quickly  de- 


Efficiency  of  Capital  Invested — Boilers 
are  used  to  earn  money,  and  what  the  boiler 
owner  wants  to  know  is  "What  boiler  from 
the  day  I  buy  it  until  it  goes  to  the  scrap 
pile  will  return  me  the  most  money  for  every 
dollar  I  invest  in  buying  and  maintaining 
it?"  Few  realize  that  while  a  boiler  may 
be  efficient  in  fuel,  it  may  still  be  a  very 
undesirable  investment.  The  chief  factors 
which  determine  the  excellence  of  a  boiler 
are,  in  order  of  their  importance:  (i) 
Safety;  (2)  Cost  of  maintenance;  (3)  Cost  of 
cleaning;  (4)  Fuel  economy;  (5)  First  cost. 

Each  of  these  has  been  so  fully  discussed 
in  its  place  that  the  further  discussion  of 
only  two  of  them  will  readily  indicate  the 
bearing  of  the  others. 


FIG.  13.     COUNTERBALANCED   STEEL  FIRE   DOORS   AND   FRAME 


stroying  the  tube,  they  affect  the  economy, 
which  rapidly  falls  off  as  the  length  of  the 
boiler  run  increases.  In  consequence  it 
will  be  found  that  after  several  weeks  the 
efficiency  reaches  a  low  figure  out  of  all  pro- 
portion to  the  efficiency  of  the  boiler  when 
clean.  The  effective  efficiency  of  the  run 
is  only  the  average  of  the  efficiencies  at  the 
beginning  and  end  of  the  run — a  fact  so 
seldom  realized  that  a  more  general  under- 
standing of  it  would  prove  of  inestimable 
benefit  to  the  boiler  purchaser. 

In  consequence  of  the  difference  between 
the  Stirling  and  other  types  in  the  manner 
of  depositing  scale,  it  will  be  found  that 
while  when  clean  the  two  types  of  boiler 
may  develop  the  same  efficiency,  the  differ- 
ence at  the  end  of  the  run  will  be  largely 
in  favor  of  the  Stirling.  Table  60,  page  208, 
gives  results  of  many  tests  on  Stirling  boilers. 


For  the  first  case  the  financial  aspect  of 
the  difference  in  time  required  for  cleaning 
the  various  types  will  be  considered.  It 
has  been  shown  that  the  time  required  to 
open,  clean,  close  and  steam  up  a  Stirling 
is  often  less  than  that  needed  simply  to 
remove  and  refit  the  caps  in  other  types. 
The  labor  costs  are  frequently  5  to  i ,  and  the 
time  the  boiler  is  off  4  to  i,  both  in  favor 
of  the  Stirling.  A  point  even  more  impor- 
tant, but  which  is  frequently  overlooked, 
is  that  every  day  a  boiler  is  off  for  repairs 
means  that  much  capital  earning  nothing, 
the  capital  being  not  only  that  invested  in 
the  boiler,  but  in  piping  connected  to  it, 
buildings  housing  it,  and  ground  upon  which 
it  stands.  Assume  that  cleaning  is  neces- 
sary every  four  weeks.  In  this  time  a  Stirl- 
ing will  be  off  one  day,  and  the  cap  types 
be  off  four  days.  The  difference,  three  days, 


CONCLUSIONS    FROM    PRECEDING   DISCUSSION 


33 


is  ten  per  cent,  of  a  month,  hence  it  follows 
that  apart  from  the  fourfold  cost  of  cleaning 
the  cap  type  boiler,  that  type  will  per  annum 
produce  ten  per  cent,  fewer  horse-power 
hours,  or  in  other  words,  for  the  same  output 
of  steam  ten  per  cent,  greater  capacity  of  cap 
type  boilers  than  Stirlings  will  be  necessary, 
disregarding  the  additional  time  lost  by  the 
cap  types,  owing  to  more  frequent  tube 
renewals. 

For  the  second  case  a  comparative  list 
of  repairs  of  different  types  as  installed  at 
the  World's  Columbian  Exposition,  Chicago, 

TABLE  1 

A  MEMORANDUM  SHOWING  CAUSES  OF  WITHDRAWAL 
FROM  SERVICE,  AND  REPAIRS,  ON  SIX  TYPES  OF 
WATER-TUBE  BOILERS,  AT  THE  WORLD'S  COLUM- 
BIAN EXPOSITION,  FROM  MAY  i  TO  NOVEMBER 
i,  1893. 


STIRLING—  2700  H.  P. 

SQUARE  HEADER 

July     5.     Caulking  Shell. 

TYPE—  1500  H.  P. 

Sep.   27.     Burned  Tube. 
Oct.   11.     Burned  Tube. 

July  12      Leaking  Tubes. 
1  8       Burned  Tubes. 

Aug.     5       Burned  Tubes. 

8      Changing  Tubes. 

SINUOUS  HEADER 

10      Changing  Tubes. 

TYPE—  3000  H.  P. 

1  1       Leaking  Tubes. 
25       Changing  Tubes. 

May   24.     Three  headers  broke, 
one  tube  burst,  No. 
7  boiler. 

Oct.   12      Putting  in  Tubes. 
15       Replacing  Tubes. 
1  8       Replacing  Tubes. 

June    i.     Tubes  out  of  order. 
3.     Bad  Tubes. 

HEADER  AND  RETURN- 

8.     Bad  Tubes. 

BEND  TYPE—  1500  H.  P. 

14.     Tubes  leaking. 
26.      Replacing  Tubes. 
July   17.      Replacing  Tubes. 
22.      Replacing  Tubes. 
Aug.  13.     Tubes  out. 
22.     Changing  Tubes. 
30.     Leaking  Tubes. 
Sep.   22.     Burned  Tubes. 
25.      Burned  Tubes. 
2Q.     Changing  Tubes. 
Oct.     8.     Leaking  Tubes. 
10.     Leaking  Tube?, 
ii.     Burned  Tubes. 
15.     Burned  Tubes. 

June  28.     Replacing  Tubes. 
July     5.     Repairing  Boiler. 
1  6.     Replacing  Tubes. 
22.      Replacing  Tubes. 
Aug.  15.     Changing  Tubes. 
30.     Leaking  Tubes. 
Sep.     8.     Leaking  Tubes. 
13.     Leaking  Tubes. 
15.     Changing  Tubes. 
215.     Leaking  Tubes. 
28.     Burned  Tubes. 
Oct.     8.     Burned  Tubes. 
17.     Burned  Tubes. 
19.     Burned  Tubes. 

24.     Burned  Tubes. 

SQUARE  HEADER 
TYPE—  3750  H.  P. 

IRREGULARLY  SHAPED 
HEADERS—  1500  H.  P. 
July     5       Repairs  on  Boilers. 

July  20.      Replacing  Tubes. 
25.      Replacing  Tubes. 
Aug.    3.     Leaking  Tubes. 
7.     Leaking  Tubes. 
29.     Two  Tubes  out. 
Sep.     o-     Burned  Tubes. 
12.     Leaking  Tubes. 

22       Burned  Tube. 
28       Repairing  Tube. 
Aug.     i       Repairs  on  Boilers. 
10       Replacing  Tubes. 
13       Replacing  Tubes. 
20       Working  on  Boilers. 
Oct.    17       Leaking  Tubes. 

14.      Burned  Tubes. 
21.     Leaking  Tubes. 

WATER-LEG  TYPE 

25.     Leaking  Tubes. 

4500  H.  P. 

Oct.      5.     Leaking  Tubes. 

Sep.   24.     Burned  Tubes. 

10.      Burned  Tubes. 

28.     Burned  Tubes. 

15.     Replacing  Tubes. 

Oct.     4.     Burned  Tubes. 

26.     Engineer     in     charge 

12.     Burned  Tubes. 

ordered  fireman  not 

15.     Burned  T'bs  in  4B'lrs. 

to  fire  No.   i   Boiler. 

22.     Burned  Tubes. 

Cause  not  known. 

26.     Burned  Tubes. 

1893,  will  be  presented,  as  evidence  of  the 
relative  durability  and  repair  account  of 
the  boilers  when  operating  under  identical 
conditions,  with  the  same  water  and  fuel. 
The  purpose  of  this  comparison  being  to 
illustrate  the  performance  of  types,  and  not 
of  particular  boilers,  the  names  of  the  various 
competing  boilers  will  be  suppressed. 

Imitations — One  of  the  strongest  testi- 
monials of  the  excellence  of  the  Stirling  boiler 
is  the  vigor  with  which  attempts  have  been 
and  are  being  made  to  imitate  it.  As  the 
circulation  in  the  Stirling  is  one  of  its  most 
prominent  advantages,  some  imitators  at- 
tempt to  reproduce  this  circulation  to  some 
degree,  but  with  an  altered  arrangement 
and  number  of  tube  banks  and  drums.  In 
other  respects  the  constructive  features 
peculiar  to  the  Stirling  boiler  are  copied  as 
closely  as  is  thought  safe. 

In  another  class  of  imitations  some  part 
of  the  Stirling  boiler, — as  for  example  two 
drums  and  their  connecting  tubes, — is  ex- 
ploited as  a  new  type  of  boiler,  and  great 
stress  is  laid  upon  the  fact  that  curved  tubes 
are  used.  While  the  curved  tubes  are  a 
great  advantage,  these  abbreviated  types 
have  merely  resurrected  many  ancient  de- 
fects which  the  Stirling  was  designed  to 
bury.  Thus,  if  the  water  is  fed  into  their 
upper  drum,  wet  steam  results;  if  fed  into 
the  lower  drum,  the  hottest  tubes  rapidly 
scale  up,  just  as  in  the  horizontal  type  of 
water-tube  boilers.  Besides  deficient  steam 
and  water  space,  none  of  these  arrangements 
even  remotely  reproduce  the  effect  of  the 
feed  drum  and  rear  bank  of  tubes  in  the 
Stirling  boiler. 

Conclusions — The  final  judgment  as 
to  the  merit  of  a  boiler  must  rest  with  those 
who,  by  long  experience  with  it,  have  as- 
certained its  virtues  or  its  failures,  and  from 
their  verdict  there  can  be  no  appeal.  When 
judged  by  this  standard,  the  finding  is  over- 
whelmingly in  favor  of  the  Stirling.  No 
other  boiler  ever  placed  upon  the  market 
has  so  quickly  met  with  popular  favor, 
retained  that  favor,  and  had  such  phenom- 
enal sales.  In  consequence  over  2,000,000 
horse-power  are  in  use,  in  all  parts  of  the 
world  where  the  value  of  human  life  and 
the  economical  generation  of  steam  are 
understood  and  appreciated. 


Water-Tube  versus  Fire-Tube  Boilers 


In  proportion  as  the  use  of  steam  has 
become  more  general  and  its  economical 
generation  has  become  better  understood 
the  water-tube  boiler  has  rapidly  displaced 
other  types,  until  it  is  now  used  exclusively 
in  all  plants  in  which  safety  and  economy 
are  considered.  Marine  engineers,  through 
excessive  conservatism,  have  been  slow  in 
adopting  the  water-tube  boiler,  but  the 
advantages  of  that  type  have  been  so  clearly 
proved  that  to-day  the  use  of  water-tube 
boilers  in  the  merchant  marine  is  rapidly 
increasing,  while  the  great  naval  powers, 
including  the  United  States,  have  adopted 
for  war  vessels  the  water-tube  boiler  to  the 
exclusion  of  other  types.  It  must,  there- 
fore, be  evident  that  the  water- tube  boiler 
possesses  advantages  which  make  it  superior 
to  the  types  it  has  displaced,  and  some  of 
these  advantages  will  now  be  set  forth. 

Safety — The  advent  of  high  pressure  was 
one  of  the  strongest  factors  in  forcing  the 
adoption  of  the  water-tube  boiler.  To  make 
this  clear,  a  gauge  pressure  of  200  Ibs.,  and 
an  allowable  stress  of  12,000  Ibs.  per  square 
inch  on  boiler  steel  will  be  assumed,  and 
neglecting  the  weakening  effect  of  joints, 
the  thickness  of  plate  necessary  for  cylinders 
of  various  diameters  will  then  be, 


DIA.  CYLINDER, 

INCHES. 

3i 
36 
48 
60 
72 
108 

I2O 
144 


THICKNESS 
INCHES. 

0  .  O2O 
0.300 

o .  400 

0.500 

o.  600 
o .  900 

1  .  OOO 
I  .  2OO 


The  rapidity  with  which  the  plate  thickness 
increases  with  the  diameter  is  apparent;  in 
practise  all  the  above  thicknesses,  except 
the  first,  have  to  be  augmented  30  to  40 
per  cent,  because  of  riveted  joints. 

In  water-tube  boilers  the  drums  seldom 
exceed  48  inches  diameter,  hence  the  thick- 
ness of  plate  required  is  never  excessive. 
The  thinner  metal  can  be  rolled  of  more 


uniform  quality,  the  seams  admit  of  better 
proportioning,  and  the  joints  can  be  more 
easily  and  perfectly  fitted  than  when  thicker 
plates  are  used. 

The  3^  inch  tube  is  a  standard  size  in  the 
Stirling  boiler,  and  for  200  Ibs.  pressure  a 
tube  of  No.  10  gauge  is  used.  The  thickness 
is  0.134  inch  and  with  the  same  working 
stress  as  used  in  computing  the  above  table 
the  safe  pressure  would  figure  1,072  Ibs. 
which  will  indicate  the  margin  of  safety. 

The  essential  constructive  difference  be- 
tween the  water-tube  and  fire-tube  types 
is  that  the  former  is  composed  of  parts  of 
relatively  small  diameter,  and  a  rupture 
of  a  part  must  of  necessity  be  local.  The 
drums  are  so  disposed  that  they  are  pro- 
tected from  intense  heat,  and  in  the  Stirling 
boiler  there  is  a  further  advantage  due  to 
elimination  of  riveted  joints  exposed  to 
high  temperature.  The  greatest  heat  strikes 
on  the  tubes,  hence  the  tubes  are  necessarily 
the  parts  which  are  most  liable  to  wear  and 
deterioration.  If  a  tube  fails  it  can  instantly 
discharge  only  the  water  it  contains,  while 
the  water  in  the  other  tubes  must  travel  a 
considerable  distance  to  reach  the  point 
of  rupture.  The  quantity  of  water  that 
can  flow  in  a  given  time  is  limited  by  the 
bore  of  the  tube,  hence  the  results  of  a  tube 
failure  may  cause  inconvenience  and  require 
a  shut  down,  but  no  considerable  damage 
to  property  can  be  don?. 

Boilers  of  the  shell  type  embody 'the  un- 
desirable necessity  of  "putting  one's  eggs 
all  in  the  same  basket.  "  Not  only  are  the 
shells  subject  to  influences  tending  far  more 
to  rupture  them  than  in  case  of  drums  in 
the  water-tube  type,  but  when  they  do 
rupture  the  whole  body  of  contained  water 
is  liberated,  and  a  disastrous  and  usually 
fatal  explosion  results.  This  is  well  evidenced 
in  a  recent  case  where  a  return  tubular  boiler 
made  by  a  leading  manufacturer,  lately 
inspected  and  declared  by  competent  au- 
thorities to  be  well  constructed,  and  free 
from  defects,  exploded  and  killed  42  persons, 
besides  causing  large  property  loss.  This 
typical  case  is  merely  one  of  a  vast  number 


QUICK   STEAMING 


37 


which  could  be  cited.  The  photograph  on 
page  36  illustrates  the  disastrous  results  of 
the  failure  of  a  small  return  tubular  boiler. 
This  boiler  was  installed  in  a  saw  mill  and 
exploded  in  November,  1904.  The  boiler 
house  and  the  brick  stack  were  both  com- 
pletely demolished,  and  an  empty  boiler 
adjoining  the  exploded  one  was  thrown 
outside  the  building  and  fell  beside  the  shed 
in  the  background.  It  must  therefore  be 
remembered  that  when  boilers  explode, 
they  wreck  not  only  themselves  but  con- 
tiguous buildings,  hence  a  water-tube  boiler, 
in  addition  to  its  other  advantages,  is  de- 
sirable as  a  matter  of  insurance  against 
explosion. 

To  the  above  mentioned  advantages  of 
the  water-tube  type  the  Stirling  boiler  adds 
additional  advantages  peculiar  to  itself. 
The  elimination  of  all  cast  metal,  compli- 
cated joints,  riveted  joints  exposed  to  fire, 
stayed  surfaces,  and  parts  of  irregular  shape, 
increases  the  element  of  safety.  A  further 
advantage  is  the  elimination  of  all  com- 
pressive  stresses.  A  cylinder  subject  to 
external  pressure,  as  a  fire-tube,  or  the  in- 
ternally-fired furnace  of  certain  types  of 
boiler,  will  collapse  under  much  less  pressure 
than  it  could  stand  if  applied  internally; 
if  any  initial  distortion  from  its  true  shape 
exists,  the  effect  of  the  external  pressure 
is  to  increase  the  distortion  and  collapse 
the  cylinder,  while  an  internal  pressure  tends 
to  restore  it  to  its  original  shape. 

Elimination  of  Temperature  Stresses — 
Stresses  due  to  unequal  expansion  have  been 
a  fruitful  source  of  trouble  in  fire-tube  boilers, 
In  water-legs,  under  internally-fired  furnaces, 
and  below  the  tubes,  the  circulation  is  de- 
fective. In  consequence,  leaks  are  common, 
and  cause  unsuspected  corrosion  in  parts 
of  the  boiler  that  are  not  visible;  stresses 
due  to  unequal  expansion  of  the  metal  cannot 
be  avoided,  and  these  are  often  so  excessive  • 
that  the  safety  of  the  boiler  is  endangered, 
and  many  a  disastrous  explosion  has  been 
traced  to  this  source. 

If  the  temperature  on  the  fire  and  water 
sides  of  a  plate  be  kept  constant,  the  rate  of 
transmission  of  heat  is,  within  reasonable 
limits,  but  little  affected  by  the  plate  thick- 
ness. In  practical  work  such  constant  tem- 
peratures are  not  maintained,  owing  to 


fluctuations  due  to  firing,  and  the  variation 
in  the  demand  for  steam.  If  the  furnace 
temperature  be  quickly  increased  in  response 
to  a  sudden  demand  for  steam,  the  plate 
itself  must  absorb  the  heat  to  elevate  its 
temperature,  hence  if  the  plate  be  thick  the 
heat  transmission  to  the  water  must  be 
sluggish,  and  the  steam  pressure  cannot  be 
quickly  increased.  An  even  more  trouble- 
some feature  in  large  shell  boilers  is  the  ab- 
solute necessity  of  firing  them  up  very 
slowly,  to  allow  their  parts  gradually  to 
expand.  This  often  takes  12  hours,  and 
besides  wasting  fuel,  it  renders  the  boiler 
useless  in  emergencies.  To  diminish  this 
evil  artificial  means  of  circulating  the  water 
are  often  used,  such  as  "  Hydrokineters " 
and  circulating  pumps,  but  they  are  merely 
slight  palliations,  and  not  remedies,  as 
evidenced  by  the  following  statement  from 
a  prominent  marine  engineer : 

"Those  of  us  who  have  had  to  do  with 
the  maintenance  of  Scotch  boilers  know 
what  a  continual  round  of  expensive  re- 
pairs have  to  be  made  at  nearly  every  in- 
spection, and  in  almost  every  case  the  causes 
are  due  to  straining  because  of  unequal 
expansion.  *  *  *  There  are  Scotch 
boilers  running  at  a  working  pressure  of  150 
Ibs.,  upon  the  bottom  of  the  shell  of  which 
the  bare  hand  may  be  placed  without  any 
inconvenience. " 

These  troubles  are  wholly  obviated  in  the 
Stirling  water-tube  boiler.  The  metal  ex- 
posed to  heat  is  thin,  hence  the  pressure 
rapidly  responds  to  an  increase  in  the  furnace 
temperature.  Circulation  is  rapid  and  takes 
place  in  a  definite  path  which  is  arranged  in 
conformity  with  the  law  of  greatest  economy. 
The  rapid  circulation  practically  equalizes 
the  temperature  in  all  parts  of  the  boiler, 
and  the  arrangement  of  parts  is  such  that 
temperature  stresses  are  eliminated.  Leaks 
and  corrosion  due  to  them  are  obviated,  and 
the  repair  bill  is  lessened. 

Quick  Steaming — The  thin  metal  in  the 
tubes  and  the  elimination  of  temperature 
stresses  in  the  Stirling  boiler  permit  steam 
to  be  raised  so  rapidly  that  in  emergencies 
the  boiler  can  be  pressed  into  service  and 
operated  at  a  high  capacity,  long  before  a 
boiler  of  the  shell  type  could  safely  be  brought 
up  to  pressure.  A  unique  illustration  of 


FORD   PLATE  GLASS   CO.,  TOLEDO,  O.,  OPERATING  4.0OO   H.  P.  OF  STIRLING   BOILERS 


EFFICIENCY   DECREASED    BY    INCRUSTATION 


39 


the  adaptability  of  the  water-tube  boiler  in 
situations  where  sudden  loads  are  to  be 
encountered  is  afforded  by  a  plant  generating 
current  for  electric  locomotives  pulling  trains 
through  a  long  tunnel.  When  no  train  is 
passing  there  is  no  load  on  the  plant,  the 
engines  turn  slowly,  and  the  boilers  have 
little  to  do.  A  few  moments  before  a  train 
arrives  a  signal  is  given,  the  draft  is  turned 
on  the  boilers,  steaming  at  full  rate  at  once 
begins,  the  engines  are  speeded  up,  and  the 
train  upon  arrival  at  the  tunnel  is  at  once 
pulled  through.  The  method  of  operating 
the  water-tube  boilers  saves  a  large  amount 
of  fuel  which  would  be  necessary  for  any 
other  type  of  boiler  which  cannot  almost 
immediately  respond  to  sudden  demands  for 
steam. 

Cleaning — In  order  that  a  boiler  may  be 
cleaned  thoroughly  it  is  necessary  that  every 
inch  of  its  interior  surface  be  accessible. 
This  requirement  cannot  be  met  in  fire-tube 
boilers.  The  tubes  are  nested  together, 
and  when  incrustation  forms  upon  them  it 
can  be  removed  only  from  such  surfaces 
as  can  be  reached.  With  a  space  between 
tubes  often  less  than  i\  inches  all  that  can 
be  done  is  to  pass  in  the  vertical  spaces  a 
thin  sharp-pointed  tool  which  can  remove 
only  a  limited  amount  of  the  deposit  on  the 
side  of  the  tube.  In  consequence  nearly 
the  entire  tube  circumference  is  inaccessible. 
The  efficiency  of  the  boiler  rapidly  falls  off, 
and  if  the  tubes  get  very  hot  they  burn,  so 
that  frequent  renewals  are  necessary.  In 
the  Scotch  marine  type,  even  when  the  engines 
operate  condensing,  tube  renewals  at  inter- 
vals of  six  to  seven  years  are  necessary,  and 
renewals  in  less  than  a  year  are  sometimes 
required.  In  return  tubulars  operated  with 
very  bad  water  annual  tube  renewals  are 
not  uncommon.  In  the  return  tubular  much 
sediment  falls  on  the  bottom  sheets  where 
owing  to  the  great  heat  it  bakes  to  such  ex- 
cessive hardness  that  the  only  method  of 
removing  it  is  to  chisel  it  out.  This  can  be 
done  only  when  sufficient  tubes  are  omitted 
to  leave  space  for  a  man  to  crawl  in,  and  the 
discomforts  under  which  he  must  work  are 
apparent.  Unless  this  deposit  be  removed, 
a  burned  and  bagged  plate  will  be  the  inevi- 
table result,  and  unless  attended  to  in  time 
an  explosion  will  follow. 


The  deposit  of  mud  in  water-legs  of  some 
types  of  boiler  is  an  active  agent  in  causing 
corrosion,  and  the  difficulty  of  removing 
this  deposit  through  hand  holes  is  well 
known.  A  complete  removal  is  practically 
impossible,  and  as  a  last  resort  to  obviate 
corrosion  it  is  common  to  make  the  bottom 
of  the  water-legs  of  copper. 

The  soot  and  fine  coal  swept  along  by  the 
draft  will  settle  in  the  fire-tubes,  and  unless 
promptly  removed  it  often  hardens  so  that 
it  must  be  cut  out  with  a  special  form  of 
scraper.  It  is  not  at  all  unusual,  when 
soft  coal  is  used,  to  find  the  fire-tubes  half 
filled  with  soot,  which  not  only  renders  use- 
less a  large  part  of  the  heating  surface,  but 
diminishes  the  draft,  so  that  it  is  difficult 
to  develop  the  heat  necessary  to  secure 
capacity  from  the  heating  surface  that  is 
left. 

The  effects  above  named  are  diminished 
in  varying  degrees  in  some  water- tube  boilers, 
but  are  wholly  obviated  in  the  Stirling.  The 
manner  in  which  this  boiler  handles  impure 
water  and  minimizes  formation  of  scale  has 
been  described  on  page  19,  and  the  methods 
of  removing  this  scale  are  given  in  the  chap- 
ter on  Boiler  Cleaning.  Every  inch  of  in- 
terior surface  can  be  reached  and  kept  clean. 

The  deposit  of  soot  on  the  outside  of  a 
horizontal  tube  is  less  than  when  deposited 
inside,  but  it  is  nevertheless  sufficient  greatly 
to  reduce  the  effective  heating  surface.  The 
nearly  vertical  tubes  in  the  Stirling  obviate 
this,  since  none  of  the  fine  material  carried 
over  by  the  draft  can  rest  on  the  tubes,  and 
the  only  deposit  will  be  the  soot  or  tarry 
matter  which  condenses  from  the  gases. 
Even  this  can  be  blown  off  while  the  boiler 
is  under  pressure,  while  to  expose  the  tube 
sheet  of  a  fire-tube  boiler  when  under  steam 
would  be  a  hazardous  risk,  because  of  the 
sudden  contraction  due  to  inrush  of  cold  air. 

Efficiency — What  a  boiler  may  do  when 
clean,  and  what  it  does  do  when  foul  are 
very  different  things,  and  the  magnitude  of 
the  difference  is  seldom  understood  by  owners 
of  boilers.  It  must  be  remembered  that  the 
moment  a  boiler  begins  work  its  heating 
surface  begins  to  foul  both  inside  and  out. 
When  a  boiler  has  been  operated  several 
months  without  cleaning  its  efficiency  may 
drop  off  by  as  much  as  30  per  cent,  or  more, 


ARMOUR    INSTITUTE,  CHICAGO,  ILL.,  OPERATING    1  , 1 5O   H.   P.  OF  STIRLING    BOILERS 


ADAPTABILITY    OF   THE    WATER-TUBE   TYPE 


41 


and  in  case  of  very  bad  water  this  result 
may  happen  in  a  much  shorter  time.  The 
results  will  be  worse  in  proportion  as  the 
deposits  form  on  the  hotter  surfaces,  yet  in 
the  return  tubular  type  the  sediment  drops 
to  the  bottom  of  the  shell,  sweeps  forward 
where  the  surfaces  are  hottest,  and  drops 
where  it  affects  the  economy  the  most.  The 
tubes  then  foul  up,  and  the  impossibility 
of  thoroughly  cleaning  them  has  been  pointed 
out.  The  readiness  with  which  deposit 
forms  on  crown  sheets  of  fire-box  boilers, 
and  the  large  furnaces  of  internally-fired 
types  is  too  well  known  to  require  comment. 

In  the  Stirling  boiler  the  action  is  entirely 
different.  The  sediment  is  removed  and 
blown  out,  and  the  scale  forms  on  the  coolest 
part  of  the  boiler,  as  explained  on  page  19, 
hence  the  initial  efficiency  is  not  only  higher 
than  in  the  other  types  because  of  the  su- 
periority of  design,  but  it  does  not  diminish 
so  rapidly  when  the  boiler  is  in  use. 

Efficiency  depends  not  only  upon  the  degree 
to  which  the  boiler  absorbs  heat,  but  also 
on  the  degree  to  which  the  furnace  can  de- 
velop the  heat  to  be  absorbed.  The  poorer 
the  fuel  the  more  impossible  it  is  to  develop 
its  heating  value  when  the  gases,  before  the 
combustion  is  completed,  come  into  contact 
with  the  shell  as  is  the  case  in  return  tubulars, 
or  with  furnace  walls  surrounded  by  water, 
as  in  internally-fired  types.  The  furnace 
must  be  practically  enclosed  in  fire-brick, 
and  this  requirement  is  perfectly  met  in  the 
Stirling  furnace.  The  matter  is  further 
discussed  in  the  chapters  on  "Fuel  Burning" 
and  "Steam  Boiler  Efficiency." 

Repairs — The  possession  of  great  strength; 
the  elimination  of  stresses  due  to  uneven 
temperatures,  and  of  leaks  and  the  corrosion 
due  to  them;  the  protection  of  the  drums 
from  external  heat;  and  prevention  of  de- 
posits on  the  hottest  tube  surfaces,  all  unite 
to  obviate  necessity  of  repairs.  The  tubes 
are  the  only  parts  in  the  Stirling  boiler  which 
may  need  renewal,  and  then  only  at  infrequent 
intervals.  Such  renewals  can  be  quickly 
and  cheaply  made.  In  fire-tube  boilers 
tube  renewals  are  a  much  more  serious  un- 
dertaking. As  the  tubes  are  enlarged  by 
accumulations  of  hard  deposit  they  cannot 
be  drawn  through  the  tube  sheet  unless  they 
are  collapsed  inch  by  inch  for  their  entire 


length;  consequently  it  is  usual  to  cut  out 
all  tubes  necessary  to  give  access  to  the  de- 
fective one,  and  the  tubes  so  cut  are  passed 
out  of  the  manhole.  In  case  of  a  bagged  or 
blistered  sheet  the  defective  part  must  be 
cut  out  by  hand,  tap  holes  be  drilled  by 
ratchets,  and  as  it  is  impossible  to  get  space 
in  which  to  drive  rivets,  a  "soft  patch"  is 
necessary.  This  is  only  the  sorriest  of  make- 
shifts, and  usually  will  result  in  requiring 
the  working  pressure  to  be  reduced,  or  a 
new  plate  to  be  put  n.  To  do  the  latter  the 
old  plate  must  be  cut  out,  a  new  one  must  be 
scribed  to  place  so  as  to  locate  rivet  holes, 
and  in  order  to  secure  room  in  which  to 
work  when  driving  rivets  the  boiler  must  be 
retubed.  The  setting  of  course  must  be  partly 
torn  down,  and  then  replaced,  so  that  the 
final  cost  wil  usually  be  considered  greater 
than  the  initial  cost  of  a  Stirling  boiler.  In 
case  of  a  rupture  the  water-tube  boiler  would 
lose  a  tube  or  two  which  can  be  quickly 
replaced;  the  fire-tube  boiler  will  be  so  com- 
pletely demolished  that  the  question  of  re- 
pairs will  be  shifted  from  the  boiler  to  the 
surrounding  property,  and  the  damage  done 
to  this  property  will  usually  exceed  many 
times  the  cost  of  a  boiler  of  a  type  which 
would  have  eliminated  all  possibility  of  the 
explosion.  The  boiler  purchaser  must  con- 
sider that  not  only  are  the  current  repairs  of 
the  Stirling  much  less  than  required  for  the 
fire-tube  types,  but  that  as  a  business  prop- 
osition it  is  not  wise  to  invest  large  sums 
m  equipment  which,  through  a  possible 
accident  to  the  boiler,  may  be  either  wholly 
destroyed,  or  so  damaged  that  the  cost  of 
repairing  it,  and  the  loss  of  business  until 
the  repairs  are  made,  would  purchase  boilers 
of  absolute  safety  and  leave  a  large  margin 
beside.  Add  to  this  the  possible  loss  of 
human  life,  and  the  true  repair  account  to  be 
considered  when  purchasing  a  boiler  will 
receive  more  consideration  than  is  usually 
accorded  to  it. 

Adaptability — The  super  ority  of  the 
water-tube  type  when  sudden  loads  are  fre- 
quent has  been  pointed  out.  It  is  often  con- 
tended that  the  fire-tube  boiler  is  preferable  to 
the  water-tube  when  operating  under  variable 
loads,  for  the  alleged  reason  that  the  greater 
amount  of  water  in  the  shell  type  acts  as  a 
reservoir  of  heat,  so  that  upon  a  reduction 


SPACE    REQUIRED    BY   STIRLING   BOILERS 


43 


in  the  steam  pressure  the  stored  heat  imme- 
diately generates  sufficient  steam  to  meet 
the  demand.  In  reply  it  need  only  be  said 
that  so  far  as  the  Stirling  is  concerned  it 
often  contains  per  square  foot  of  heating 
surface,  or  per  horse-power,  as  much  water 
as  the  return  tubular,  and  much  more  than 
some  other  types.  Apart  from  this,  the 
argument  is  also  unsound.  The  total  heat 
of  steam  at  150  Ibs.  gauge  pressure  is  1193.5 
B.  T.  U.,  and  at  100  Ibs.,  1184.9  B.  T.  U.; 
difference  8.9  B.  T.  U.  As  the  latent  heat 
of  steam  at  100  Ibs.  gauge  is  876.5  B.  T.  U. 
it  will  be  seen  that  a  drop  of  50  pounds 
would  be  necessary  to  provide  heat  enough 
to  evaporate  only  one  per  cent,  of  the  water 
in  the  boiler,  consequently  a  drop  of  sufficient 
magnitude  to  have  any  practical  influence 
in  generating  extra  steam  would  go  beyond 
the  limits  which  any  engineer  would  tolerate. 
The  locomotive  boiler,  which  is  subjected  to 
violent  fluctuations  of  load  often  contains 
not  over  one-third  as  much  water  as  a  Stirling 
boiler  developing  the  same  power 

A  defect  of  all  shell  types  of  boiler  is  that 
once  they  are  built  there  can  be  no  adjust- 
ment of  draft  areas  to  suit  either  the  chimney 
to  which  the  boilers  are  attached  or  the 
fuel  which  is  to  be  burned.  Many  water- 
tube  boilers  are  equally  faulty  in  this  re- 
spect. In  the  Stirling  boiler  it  is  possible 
to  adjust  the  draft  area  to  suit  any  condi- 
tions by  shortening  or  lengthening  the  firetile 
baffles.  To  do  this  it  is  necessary  merely  to 
take  out  or  to  add  on  a  few  tiles,  without 
changing  bridge  walls,  or  flame  plates,  or 
other  parts  difficult  of  access  or  expensive 
to  alter.  Consequently  it  is  the  work  of 
only  a  few  hours  to  adjust  the  draft  areas 
in  the  Stirling  to  suit  any  new  fuel  which 
may  have  to  be  used,  while  such  adjustment 
cannot  be  made  at  all  in  any  type  of  fire- 
tube  boiler. 

Space — The  cost  of  a  boiler  plant  must 
include  not  only  the  boilers  but  the  ground, 
the  buildings,  piping,  stacks,  breechings, 
coal  bins,  and  everything  else  required  to 
complete  the  plant  ready  to  run.  Obviously 
a  saving  in  space  occupied  by  the  boiler 


will  effect  a  saving  in  piping  and  buildings. 
The  Stirling  boi.er  occupies  so  much  less 
space  than  that  required  by  fire-tube  boilers 
of  the  same  capacity  that  the  saving  thus 
made  possible  will  often  amount  to  consid- 
erable percentage  of  the  cost  of  the  boilers. 
For  example,  175  H.  P.  is  about  the  limit 
of  size  of  the  return  tubular;  a  boiler  of  that 
capacity  would  be  78  inches  diameter  and  18 
ft.  long,  and  when  erected  the  setting  would 
require  a  space  23  ft.  long  and  9  ft.  6  inches 
wide.  A  Stirling  boiler  of  the  same  capacity 
can  be  installed  in  a  space  16  ft.  3  inches  long 
by  10  ft.  wide,  18  ft.  10  inches  long  by  7  ft. 
wide,  or  in  other  lengths  and  widths  to  con- 
form to  the  requirements. 

In  large  installations  the  showing  is  still 
more  marked  in  favor  of  the  Stirling:  thus 
three  of  the  above  tubulars  would  require 
a  space  26  feet  6  inches  wide  by  23  feet  deep. 
The  equivalent  525  H.  P.  of  Stirlings  would 
require  a  space  23  by  16  feet,  or  17  by  19 
feet,  or  intermediate  widths  and  depths. 
Similarly,  six  of  these  tubulars  would  require 
a  space  52  by  23  feet,  while  equivalent 
Stirling  boilers  could  be  placed  in  a  space 
varying  from  35  by  17  feet  to  29  by  19  feet. 
The  additional  aisle  space  at  the  ends  and 
rear  would  be  the  same  for  both.  Because 
of  the  greater  space  required  by  shell  boilers 
an  attempt  is  often  made  to  increase  their 
heating  surface  by  crowding  the  tubes  very 
close.  The  effect  of  this  is  to  increase  the 
difficulty  of  removing  scale  from  the  tubes, 
and  to  cause  excessive  moisture  in  the  steam. 

Should  the  growth  of  the  plant  require 
the  substitution  of  larger  boilers  the  water- 
tube  type  can  be  taken  apart,  removed  and 
replaced  by  larger  units,  without  alteration 
of  buildings,  and  installation  of  expensive 
tackle.  This  is  an  item  of  great  importance 
when  boilers  are  installed  under  buildings, 
since  fire-tube  boilers  installed  in  such  places 
usually  cannot  be  taken  out,  without  either 
cutting  them  to  pieces  or  tearing  down  parts 
of  the  building. 

Other  important  advantages  of  the  water- 
tube  over  the  fire-tube  boilers  will  be  pointed 
out  in  the  chapters  which  follow. 


Z    ui 


Works  of  The  Stirling  Company 


The  Stirling  Company  manufactures  Water- 
Tube  Safety  Boilers  for  both  stationary  and 
marine  use,  superheaters,  chain  grates,  bag- 
asse furnaces  and  conveyors,  stacks,  breech- 
ings,  etc.  Its  works  are  located  at  Barber- 
ton,  Ohio,  and  occupy  60  acres;  the  shop 
floor  space  under  roof  is  300,000  square  feet; 
there  are  24  separate  shops,  and  28  other 
buildings.  The  shops  and  offices  are  con- 
structed of  steel,  brick,  slate,  and  wood,  on 
concrete  foundations,  and  reflect  the  highest 
development  in  American  factory  construc- 
tion. Fire  protection  is  afforded  by  the 
automatic  sprinkler  system,  and  fire  hy- 
drants located  throughout  the  grounds. 
These  connect  with  the  Company's  private 
system  of  fire  mains  and  pumps,  and  the 
City  Service  can  be  used  in  addition  if  nec- 
essary. 

The  Works  were  started  in  1890,  since 
which  time  their  valuation  and  capacity 
have  increased  over  tenfold,  yet  the  steady 
growth  of  the  Company's  business  is  such 
that  constant  additions  to  the  equipment 
are  demanded.  Already  the  plant  is  the 
largest  in  the  world  which  is  devoted  ex- 
clusively to  manufacture  of  water-tube  boil- 
ers. The  boilers  supplied  by  the  Company 
are  manufactured  in  its  own  Works,  under 
the  superintendence  of  its  own  engineers.  All 
material  is  rigidly  tested,  and  every  precau- 
tion that  years  of  experience  can  suggest  is 
taken  to  insure  that  both  the  material  and 
the  workmanship  of  these  boilers  are  of  the 
highest  grade  obtainable. 

All  parts  of  the  plant  are  provided  with 
standard  gauge  railway  tracks  and  switches, 
and  the  Company  owns  an  excellent  equip- 
ment of  locomotive  cranes,  cars,  and  buggies 
adapted  to  the  special  service  to  be  performed. 


A  unique  feature  of  the  works  is  an  immense 
gantry  crane  with  double  cantilever  arms 
spanning  the  entire  drum  yard.  Another 
overhead  crane  operates  through  a  distance 
of  600  feet  from  the  foundry  to  the  fitting 
shop,  and  passes  directly  into  both  buildings. 

The  Works  are  equipped  with  steam, 
electric,  hydraulic  and  pneumatic  power 
supplied  from  a  central  station,  and  all 
buildings  are  electric  lighted.  The  shop 
tools  are  for  the  most  part  electrically  driven, 
while  hydraulic  power  is  used  for  riveting 
and  flanging,  and  pneumatic  power  for 
caulking,  etc. 

Many  of  the  tools  have  been  designed  by 
the  Company  and  embody  every  known 
improvement  for  accomplishing  the  result 
for  which  they  are  intended.  The  entire 
equipment  is  a  striking  example  of  modern 
American  practise  in  economizing  labor  and 
material,  and  the  Company  is  ever  on  the 
alert  to  adopt  any  method  or  improvement 
which  may  reduce  cost  of  manufacture  or 
increase  the  excellence  of  its  product. 

In  addition  to  the  Stirling  boiler  as  de- 
scribed in  this  catalog,  the  Company  is  ex- 
tensively engaged  in  the  manufacture  of 
water-tube  boilers  specially  designed  for 
marine  use,  and  has  already  installed  this 
type  of  boiler  in  the  Russian  cruiser  Variag, 
the  Russian  battleship  Retvizan,  the  United 
States  battleships  Maine,  Virginia  and 
Georgia,  the  cruisers  Colorado  and  Pennsyl- 
vania, the  monitor  Nevada,  the  Imperial 
Ottoman  cruiser  Medjidia,  a  private  steam 
yacht,  and  several  of  the  largest  vessels  in 
use  in  the  merchant  marine.  Work  is  now 
actively  progressing  on  boilers  for  several 
steamships  under  construction  for  service  on 
the  Great  Lakes. 


Heat 


Heat  is  a  condition  of  matter  caused  by 
vibratory  motion  among  its  particles.  Very 
hot  bodies  are  those  in  which  the  vibrations 
are  very  rapid,  and  the  hotter  the  body, 
the  more  rapid  the  vibrations. 

Temperature — The  temperature  of  a 
body  is  the  measure  of  its  capability  of 
communicating  to  adjacent  bodies  sensible 
heat,  or  heat  that  may  be  felt.  When  two 
bodies  of  different  temperature  are  placed 
into  contact  the  hotter  body  becomes  cooler, 
and  the  colder  body  hotter,  until  finally 
their  temperatures  equalize.  This  proves 
that  heat  can  be  transferred. 

Heat  Effects — When  heat  is  added  to 
or  taken  from  a  body,  either  the  temperature 
of  the  body  is  altered,  or  its  volume  is  varied, 
or  its  state  is  changed.  Thus,  if  heat  be 
added  to  water  under  atmospheric  pressure,- 
the  temperature  of  the  water  increases  until 
it  reaches  212°  F.  If  more  heat  be  added 
and  the  pressure  remains  unchanged,  the 
temperature  does  not  further  increase,  but 
the  water  evaporates  into  steam.  Heat 
thus  changes  water  from  a  liquid  to  a  gaseous 
state.  If  heat  be  abstracted  from  water 
the  temperature  is  reduced  until  it  reaches 
32°  F.,  after  which  any  diminution  of  heat 
does  not  further  decrease  the  temperature, 
until  the  liquid  is  converted  into  a  solid,  or 
ice.  The  quantity  of  heat  passing  from  one 
body  to  another  can  thus  be  estimated  by 
the  effects  produced.  Therefore  heat  is 
something  that  can  be  both  transferred  and 
measured. 

The  general  effect  of  heat  on  a  body  is 
to  increase  its  volume.  If  heat  be  abstracted 
from  a  body  the  contrary  effect  ensues, 
and  the  volume  is  diminished.  Hence  the 
general  principle,  to  which,  however,  there 
are  some  exceptions,  that  heat  expands  and 
cold  contracts.  These  effects,  arising  from 
a  change  of  temperature,  are  produced  in 
very  different  degrees  according  to  the  nature 
of  the  bodies.  They  are  small  in  solids, 
greater  in  liquids,  and  greater  still  in  gases. 

It  is  well  known  that  the  work  expended 
in  friction  apparently  is  lost  as  regards 
mechanical  work;  that  heat  is  developed 


when  friction  occurs;  that  the  greater  the 
friction  the  greater  is  the  amount  of  heat 
produced.  Experiments  have  proved  that 
the  amount  of  heat  generated  by  friction 
is  exactly  equivalent  to  the  amount  of  work 
lost,  whence  it  is  shown  that  heat  like  me- 
chanical work  is  one  of  the  forms  of  energy. 
Thermometers — In  consequence  of  the 
uniform  expansion  of  mercury  and  its  great 
sensitiveness  to  heat,  it  is  the  fluid  most 
commonly  used  in  the  construction  of  ther- 
mometers. In  all  thermometers  the  freez- 
ing and  the  boiling  point  of  water,  under 
mean  atmospheric  pressure  at  sea  level, 

TABLE   2 
COMPARISON    OF    THERMOMETER    SCALES 


Fahrenheit 

Centigrade 

Reaumur 

Absolute  Zero  .    .    . 

-460  .  66 

-273.70 

-218.96 

0 

-17.77 

-14.  22 

IO 

-12.23 

-9-77 

20 

-6.67 

-5-33 

3° 

—  I  .  I  I 

-0.88 

Freezing  Point     .    . 

32 

0. 

o  . 

Maximum  Density  I 

of  Water  .    .    /  f 

39  -i 

3-94 

3-J5 

5° 

10. 

8. 

75 

23.89 

19.11 

IOO 

37-78 

30.22 

200 

93-34 

74.66 

Boiling  Point    .    .    . 

212 

IOO. 

80. 

250 

121  .  II 

96.88 

300 

148.89 

119.11 

350 

176.67 

141-33 

F  -  i  e  +  32°  =  i  R  +  32° 

C  =  5  (F  -  32°)  -  3  R. 
R  =  I  C  =  *  (F  -  32°). 

are  assumed  as  two  fixed  points,  but  the 
division  of  the  scale  between  these  two  points 
varies  in  different  countries,-  hence  there 
are  in  use  three  thermometers,  known  as 
the  Fahrenheit,  the  Centigrade  or  Celsius, 
and  the  Reaumur.  In  the  Fahrenheit  the 
space  between  the  two  fixed  points  is  divided 
into  1 80  parts;  the  boiling  point  is  marked 
212,  and  the  freezing  point  is  marked  32, 


47 


48 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


and  zero  is  a  temperature  which,  at  the  time 
this  thermometer  was  invented,  was  incor- 
rectly imagined  to  be  the  lowest  temperature 
attainable.  In  the  Centigrade  and  the  Reau- 
mur scales  the  distance  between  the  two 
fixed  points  is  divided  into  100  and  80  parts, 
respectively.  In  each  of  these  two  scales 
the  freezing  point  is  marked  o,  and  the  boiling 
point  is  marked  100  in  the  Centigrade,  and 
80  in  the  Reaumur.  Each  of  the  180,  100, 
or  80  divisions  in  the  respective  thermom- 
eters is  called  a  degree. 

Table  2  and  appended  formulas  are  useful 
for  converting  from  one  scale  to  another: 

Absolute  Zero — Experiments  show  that 
at  32°  F.  a  perfect  gas  expands  4921.66  part 
of  its  volume  if  its  pressure  remains  constant, 
and  its  temperature  is  increased  one  degree. 
If  this  rate  of  expansion  per  degree  held 
good  at  all  temperatures  (and  experiment 
shows  that  it  does  above  the  freezing  point), 
the  gas,  if  its  pressure  remained  the  same, 
would  double  its  volume  if  raised  to  a  tem- 
perature of  32  +  492.66=524.66  Fah.,  while 
under  a  diminution  of  temperature  it  would 
shrink  and  finally  disappear  at  temperature 
of  492.66-32=460.66°  below  zero  Fah. 
While  undoubtedly  some  change  in  the  law 
would  take  place  before  the  lower  temper- 
atures could  be  reached,  this  is  no  reason 
why  the  law  may  not  be  used  within  the 
range  of  temperatures  where  it  is  known  to 
hold  good.  From  the  preceding  explanation 
it  is  evident  that,  under  a  constant  pressure, 
the  volume  of  a  gas  will  vary  as  the  number 
of  degrees  between  its  temperature,  and  the 
temperature  of — 460. 66 J  Fah.  To  simplify 
the  application  of  the  law,  a  new  thermomet- 
ric  scale  is  constructed  as  follows:  the  point 
corresponding  to  — 461°  F.  is  taken  as  the 
zero  point  on  the  new  scale,  and  the  degrees 
are  identical  in  magnitude  with  those  on 
the  Fahrenheit  scale.  Temperatures  re- 
ferred to  this  new  scale  are  called  absolute 
temperatures,  and  the  point  — 461°  F.  (= 
-273  C)  is  called  the  absolute  zero.  To  convert 
any  temperature  Fahrenheit  to  absolute 
temperature,  add  461  to  the  temperature 
on  the  Fahrenheit  scale;  thus  54°  F.  will  be 
54r46i==5i5°  absolute  temperature;  113° 
F.  will  likewise  be  equal  to  113  +  461 
574°  absolute  temperature.  If  one  pound  of 
gas  had  a  temperature  of  54°  F.,  and  another 


pound  had  a  temperature  of  113°  F.,  the 
respective  volumes  would  be  in  the  ratio  of 
515  to  574,  if  the  pressure  on  each  were  the 
same. 

British  Thermal  Unit  —  The  quanti- 
tative measure  of  heat  is  the  British  Thermal 
Unit.  It  is  ordinarily  written  B.  T.  U., 
and  is  the  quantity  of  heat  required  to  raise 
the  temperature  of  a  pound  of  pure  water 
one  degree,  at  its  point  of  maximum  density, 
viz.:  39.1°  F.  In  the  metric  system  the 
unit  is  the  calorie,  or  the  heat  necessary  to 
raise  the  temperature  of  a  kilogramme  of 
water  one  degree  Centigrade,  at  the  point 
of  maximum  density. 

i  B.  T.  U.=.2$2  Calorie 
_       B.  T.  U. 


Specific  Heat  —  The  quantity  of  heat 
required  to  raise  the  temperature  of  unit 
weight  of  any  substance  one  degree  varies 
with  the  substance,  and  is  called  the  specific 
heat  of  that  substance.  It  is  also  the  ratio 
of  the  heat  so  required  to  that  required  to 
heat  the  same  weight  of  water.  For  solids, 
at  ordinary  temperatures,  the  specific  heat 
is  constant  for  each  individual  substance, 
although  it  is  variable  at  high  temperatures. 
In  the  case  of  gases  a  distinction  must  be 
made  between  specific  heat  at  constant 
volume,  and  a  constant  pressure. 

Where  merely  specific  heat  is  stated  it 
implies  specific  heat  at  ordinary  temperature, 
and  mean  specific  heat  refers  to  the  average 
value  of  this  quantity  between  the  tem- 
peratures named. 

The  specific  heat  of  a  mixture  of  gases 
is  obtained  by  multiplying  the  specific  heat 
of  each  constituent  gas  by  the  percentage 
of  that  gas  in  the  mixture,  and  dividing  the 
sum  of  the  products  by  100.  The  specific 
heat  of  a  gas  whose  composition  is  CO,  13; 
COg,  0.4;  0,  8;  N,  7  8.  6.  is  found  as  follows: 

CO,      13          X.2I7  2.  821 

COZ,   0.4    X.2479   =  .09916 

0,      8       X.  21751=         1.74008 
N,  78.6  X.2433  =        19.16268 
100.  o  23.82292 

and    23.8229-^100  =  .238  =  specific    heat    of 
this  gas. 

Latent  Hea  t  —  Where  the  application 
of  heat  results  in  a  change  of  state  of  a  sub- 
stance, either  from  solid  to  liquid,  or  from 


BOILING    POINT    OF    LIQUIDS 


49 


liquid  to  gaseous,  there  is  an  absorption  of 
heat  without  any  rise  in  temperature,  and 
the  heat  thus  absorbed  is  termed  latent 
(or  hidden),  because  it  apparently  disappears, 
and  is  not  measurable  by  a  thermometer. 
It  is  not  lost,  but  reappears  whenever  the 
substance  passes  through  the  reverse  cycle, 
from  a  gaseous  to  liquid,  or  from  a  liquid 
to  a  solid  state.  Latent  heat  is  therefore 

TABLE   3 
SPECIFIC   HEATS 

SOLIDS. 

Copper .  -Q951 

Gold 0324 

Wrought  Iron 1138 

Cast  Iron 1298 

Steel  (soft) 1165 

Steel  (hard) •     -"75 

Zinc .0956 

Brass °939 

Glass IQ37 

Lead 0314 

Platinum 03  24 

Silver 0570 

Tin 0562 

Ice 5040 

Sulphur 2026 

Charcoal 2410 


LIQUIDS. 

Water 

Alcohol          

Mercury 

Benzine         

Glycerine 

Lead  (melted) 

Sulphur  (melted) 

Tin  (melted)       .... 

Sulphuric  Acid 

Oil  of  Turpentine 

GASES. 

Air  (at  freezing  point) 

Oxygen        

Nitrogen 

Hydrogen 

Superheated  steam*    . 
Carbon  Monoxide -(CO)     . 
Carbon  Dioxide  (CO2) 
Olefiant  Gas      .... 
Blast  Furnace  Gas 
Chimney  Gases  (approx.) 


.0000 
.  7000 

•0333 
.4500 

•555° 
.  0402 

.2340 
.0637 

•335° 
.4260 


At  Constant 
Pressure. 

At  Constant 
Volume. 

•2375 

.1685 

•2175 
.2438 

•I551 
.1727 

3.4090 
.4805 
.2479 

2.4123 
•346 

•1758 

.  2170 

•IS35 

.  4040 
.2277 

•J73 

II 
.  2/tO 

the  quantity  of  heat  which  apparently  dis- 
appears, or  is  lost  to  thermometric  measure- 
ment, when  the  molecular  constitution  of 
body  is  being  changed.  It  is  expended  in 
performing  the  work  of  overcoming  the  molec- 
ular cohesion  of  the  particles  of  the  sub- 
stance, and  in  overcoming  the  resistance  of 
external  pressure  to  change  of  volume  of  the 
heated  body. 

If  heat  be  applied  to  a  pound  of  ice  there 
will  be  a  rise  in  temperature  until  the  freezing 
point,  32°  F.,  is  reached.  The  ice  will  then 
begin  to  melt,  but  the  temperature  of  the 
mixture  of  ice  and  water  will  remain  32° 
F.,  as  long  as  any  particle  of  ice  remains  in 
it.  Yet  the  melting  process  will  absorb 
heat.  The  amount  thus  absorbed  in  changing 
the  state  of  a  pound  of  ice  from  ice  at  32° 
F.,  to  water  at  32°  F.  is  144  B.  T.  U.  This 
is  the  latent  heat  of  fusion  of  ice.  If  the 
application  of  heat  be  continued  the  tempera- 
ture of  the  water  will  rise,  but  it  will  now 
require  about  twice  as  many  heat  units  to 
effect  a  rise  of  one  degree  as  it  did  to  accom- 
plish the  same  rise  in  the  ice.  The  reason 
is  that  the  specific  heat  of  water  is  i.oo, 
while  that  of  ice  is  only  .504.  When  the 
water  has  reached  a  point  of  212°  F.,  there  is 
a  further  absorption  of  heat  with  no  increase 
of  temperature.  Boiling  occurs,  and  the 
heat  absorbed  is  expended  in  transforming 
the  water  into  steam.  Water  at  atmos- 
pheric pressure  cannot  be  heated  beyond 
212°  F.,  and  the  steam  which  is  formed  is 
also  at  a  temperature  of  212°  F.,  when  the 
entire  pound  of  water  has  been  evaporated 
into  steam,  965.8  B.  T.  U.  have  been  usedin 
the  operation.  This  is  the  latent  heoi  of 
evaporation  of  water. 

Ebullition — The  temperature  of  ebulli- 
tion of  any  liquid,  or  its  boiling  point, 
may  be  defined  as  that  stage  in  the  addition 

TABLE    4 

BOILING    POINTS    AT     ATMOSPHERIC 

PRESSURE  (Kent) 
(14.7  Ibs.  absolute  per  square  inch.) 

Ammonia.  140°  F.  Water 212°  F. 

Bromin.  .  .  145  Average  sea  water  213.2 

Alcohol.  .  .173  Saturated  brine.  .226 

Benzine.  ..212  Mercury 676 


*The  specific  heat  of  superheated  steam  is  variable.     See  page  93. 


50 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


of  heat  to  the  liquid  at  which  the  temperature 
of  the  liquid  is  no  longer  increased  and  the 
heat  added  is  absorbed  by  converting  the 
liquid  into  vapor.  This  temperature  de- 
pends upon  the  pressure  under  which  the 
liquid  is  evaporated;  the  greater  the  pressure 
the  higher  the  temperature. 

Heat  of  the  Liquid — In  the  evaporation 
of  any  liquid,  that  quantity  of  heat  which 
is  absorbed  in  raising  the  temperature  from 
32°  F.  to  the  temperature  of  ebullition  cor- 
responding to  the  particular  pressure  at  which 
the  evaporation  occurs,  is  the  sensible  heat, 
or  the  heat  of  the  liquid. 

Total  Heat  of  Evaporation — The  quan- 
tity of  heat  required  to  raise  a  unit  weight 
of  any  liquid  from  the  freezing  point  to  a 
given  temperature,  and  entirely  to  evaporate 
it  at  that  temperature  is  the  total  heat  of 
evaporation  of  the  liquid  for  that  particular 
temperature.  It  is  the  sum  of  the  heat  of 
the  liquid,  and  the  latent  heat  of  evaporation. 
To  recapitulate:  The  heat  added  to  a 
body  is  divided  up  as  follows: 

Total  Heat  =  Heat  to  change  the  tempera- 
ture +  heat  to  separate  the 
molecules  +  heat  to  over- 
come the  external  pressure 
resisting  an  increase  of  volume 
of  the  body. 

In  case  of  water  which  is  converted  into 
steam  the  total  heat  is  divided  as  follows: 
Total  Heat  =Heat  to  change  the  tempera- 
ture   of    the    water    +    heat 
to    separate  the  molecules  of 
the   water    +    heat   to    over- 
come   resistance    to    increase 
in  volume  of  the  steam. 
=Heat   of  the   liquid   +   inner 
latent    heat    4-    outer  latent 
heat. 
=Heat   of   the   liquid    +  total 

latent   heat   of   steam. 
=  Total  heat  of  evaporation. 
The  Steam  Tables,  page  74  give  the  heat  of 
the  liquid  and  total  latent  heat  through   a 
wide  range  of  temperatures. 

( I  a  s  e  s — When  heat  is  added  to  gases 
there  is  no  inner  work  to  be  done,  hence  the 
total  heat  is  that  required  to  change  the 
temperature  plus  that  required  to  do  the 
outer  work.  If  the  gas  is  not  allowed  to 
expand,  as  in  case  of  gases  heated  at  constant 


volume,    the    entire    heat    added    is  that  re- 
quired to    change   the  temperature   only. 
Mechanical  Equivalent  of    Heat — The 

relation  between  heat  and  mechanical  work 
has  been  experimentally  determined  by  Joule, 
who  found  that  the  heat  necessary  to  raise 
the  temperature  of  one  pound  of  water  one 
degree  Fahr.  at  its  maximum  density  can 
perform  work  equal  to  the  raising  of  772 
pounds  one  foot  high.  This  relation  between 
heat  and  mechanical  work  is  called  the 
mechanical  equivalent  of  heat,  or  Joule's 
equivalent.  The  latest  experimental  deter- 
mination of  Rowland  shows  that  the  exact 
value  is  somewhat  higher  than  772,  and  778 
foot-pounds  is  now  usually  accepted  as  the 
correct  mechanical  equivalent. 

Transfer  of  Heat — Heat  may  be  com- 
municated from  one  body  to  another  in  three 
different  ways:  viz.,  by  radiation,  conduction 
and  convection.  Radiation  is  the  transfer  of 
heat  between  bodies  separated  by  a  trans- 
parent medium.  Conduction  is  the  transfer 
or  flow  of  heat  from  a  hotter  to  a  colder  par- 
ticle in  contact  with  it.  Convection  is  the 
transfer  of  heat  caused  by  the  rise  of  heated 
particles  in  a  mass  of  liquid  or  gas.  The  trans- 
fer of  heat  from  a  furnace  to  the  boiler  takes 
place  by  radiation,  convection  and  conduction 
and  the  heat  is  distributed  through  the  mass 
of  water  by  convection,  but  the  exact  laws 
governing  these  methods  of  transfer  are 
unknown. 

Temperature  of  Fire — The  following  ta- 
ble, compiled  by  M.  Pouillet,  will  enable  the 
approximate  temperature  of  a  fire  to  be 
judged  by  its  appearance.  The  temperature 
is  practically  the  same  for  all  kinds  of  com- 
bustibles under  similar  conditions. 


TABLE   5 


APPEARANCE 


OF  FIRE. 

Red,  just  visible 

"     dull     .      .      . 

"     cherry,  dull    . 

"       full    . 

clear 

Orange,  deep    . 
clear   . 

White  heat        .      . 
"        bright     . 
"       dazzling 


TEMPERATURE 
FAHR. 

977° 
1290 
1470 
1650 
1830 

2010 
2IQO 
2370 

255° 
2730 


MERCURIAL    PYROMETERS 


51 


Linear  Expansion  of  Substances  by 
Heat — To  find  the  increase  in  the  length  of  a 
bar  of  any  material  due  to  an  increase  of  tem- 
perature, multiply  the  number  of  degrees  of 
increase  of  temperature  by  the  co-efficient 
for  100°  (Table  6)  and  by  the  length  of  the 
bar,  and  divide  by  100. 

The  expansion  of  metals  per  degree  rise  of 
temperature  increases  slightly  as  higher 
temperatures  are  reached,  but  for  all  practical 
purposes  it  may  be  assumed  to  be  constant. 


1 i )  Mercurial  Pyrometer  for  temperatures 
up  to  800°  Fahrenheit. 

( 2 )  Exp ansion  Pyrometer  for  temperatures 
up  to  1,500°  Fahrenheit. 

(3)  Melting  points  of   metals  which  flow 
at  various  temperatures  up  to  the    melting 
point  of  platinum,  3,227°  Fahrenheit. 

(4)  Le     Chatelier's     thermo-electric      py- 
rometer  for   temperatures   up    to    2,900°    F. 

(5)  Calorimetry  for  temperatures    up    to 
2,000°  Fahrenheit. 


TABLE    6 

LINEAR  EXPANSION  OF  SOLIDS   AT  ORDINARY  TEMPERATURES 
(The  tabular  values  are  the  fractional  increase  in  length  for  a  temperature  increase  of   iooc 

Fahrenheit  or  Centigrade.) 


NAME    OF    SUBSTANCE. 

COEFFICIENT 
PER    100° 
FAHRENHEIT. 

COEFFICIENT 
PER    IOO° 
CENTIGRADE. 

Brass   (cast)          

OOIO4 

00l88 

Brass,  (wire)  

.  OOIO7 

.  OOI  Q3 

Brick   (fire)     .                   

OOO3 

oooc 

Copper,      

.  OOOQ 

.0017 

Glass  (English  Flint)            ...            

OOO4.!; 

00081 

Glass,  (French  white  lead)   

00048 

'  .  00087 

Gold     

.  OOO8 

.  001  «; 

Granite   (average)     

OOO47 

00085 

Iron   (cast)                        ....             

OOO6 

OOI  I 

Iron   (soft  forged)      

.  OOO7 

OOI  2 

Iron   (wire)     

OOO8 

0014 

Lead    

OOl6 

0029 

Mercury    

OO3  3 

0060 

Platinum  

ooo? 

0009 

Sandstone       

0006 

OOI  I 

Silver  

OOI  I 

OO2 

Slate,  (Wales)       

0006 

OOI 

Water,  (varies  considerably  with  the  temperature)    .... 

.0086 

•0155 

High  Temperature   Measurements — 

The  temperatures  to  be  dealt  with  in  steam 
boiler  practise  range  from  those  of  ordinary 
air  and  steam  to  the  temperatures  of  burning 
fuel.  The  gases  of  combustion,  originally 
at  the  temperature  of  the  furnace,  cool  down 
as  they  pass  through  each  successive  bank 
of  tubes  in  the  boiler,  to  nearly  the  tem- 
perature of  the  steam,  resulting  in  a  wide 
range  of  temperatures  through  which  definite 
measurements  are  sometimes  required. 

Of  the  different  methods  devised  for 
ascertaining  these  temperatures,  five  of 
the  most  important  will  be  mentioned,  viz.: 


Mercurial  Pyrometers — Mercury  boils 
at  676°  F.  and  atmospheric  pressure,  and  for 
temperatures  above  500°  F.  the  ordinary 
mercurial  thermometer  cannot  be  used. 
For  higher  temperatures,  up  to  800°  F., 
the  space  above  the  mercury  is  filled  with 
nitrogen  gas,  and  as  the  mercury  expands, 
the  gas  is  compressed,  increasing  the  pressure 
and  raising  the  boiling  point.  So  constructed, 
mercurial  pyrometers  can  be  used  for  indi- 
cating temperatures  not  exceeding  800°  F. 

Flue-gas  temperatures  are  nearly  always 
taken  with  such  thermometers.  The  bulb 
of  the  instrument  should  project  into  the 


52 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


path  of  maximum  velocity  of  the  gases  in 
order  that  the  average  temperature  may 
be  obtained,  and  before  a  reading  is  taken, 
it  is  necessary  to  keep  the  thermometer 
inserted  in  the  flue  socket  from  seven  to 
fifteen  minutes  depending  on  conditions. 
Sometimes  these  thermometers  are  made 
so  that  they  can  be  permanently  attached 
to  the  wall  of  the  breeching  or  flue. 

This  is  the  most  accurate  and  by  far  the 
most  preferable  method  of  recording  stack 
and  uptake  temperatures. 

Expansion  Pyrometers — Brass  expands 
about  50%  more  than  iron  for  the  same 
increase  in  temperature;  and  for  both  the 
expansion  is  nearly  proportional  to  the  rise. 
In  expansion  pyrometers  this  phenomenon 
is  utilized  by  enclosing  a  brass  rod  in  an 
iron  pipe,  one  end  of  the  rod  being  rigidly 
attached  to  a  cap  at  the  end  of  the  pipe,  and 
the  other  end  connected  by  a  multiplying 
gear  to  a  pointer  moving  around  a  graduated 
dial.  The  whole  length  of  the  pipe  must 
be  at  a  uniform  temperature  before  the  full 
amount  of  expansion  is  obtained.  This, 
together  with  the  fact  that  lost  motion  is 
likely  to  exist  in  the  mechanism  connected 
to  the  pointer,  makes  the  expansion  pyrom- 
eter unreliable;  it  is  only  when  the  instru- 
ment is  thoroughly  understood  and  care- 
fully calibrated  that  it  can  be  depended 
upon.  Its  action  is  anomalous;  for  instance, 
if  it  is  allowed  to  cool  after  being  exposed 
to  a  high  temperature,  the  needle  will  rise 
higher  before  it  begins  to  fall.  Similarly, 
a  rise  in  temperature  is  first  shown  by  the 
instrument  as  a  fall.  The  explanation  is 
that  the  iron,  being  on  the  outside,  heats 
or  cools  more  quickly  than  the  brass.  The 
readings  are,  therefore,  valueless  unless  both 
the  brass  and  iron  are  known  to  be  of  the 
same  temperature. 

Melting  Points  of  Metals — When  an 
approximate  temperature  is  sufficient  it 
can  be  found  by  introducing  into  the  furnace 
or  flue  various  metals  of  known  melting 
points.  The  more  common  metals  form  a 
series  in  which  the  respective  melting  points 
differ  by  less  than  100°  to  200°  F.  and  by 
using  these  in  order,  the  temperatures  can 
be  fixed  between  the  melting  points  of  some 
two  of  them.  This  method  lacks  accuracy, 
but  it  suffices  very  well  for  approximate 


determination  of  the  temperatures  of  the 
furnace,  and  in  different  parts  of  the  tubes 
of  a  boiler. 

TABLE    7 

APPROXIMATE    MELTING    POINTS 
OF    METALS 

Fah. 


Wrought  Iron  melts  at  about 

2825° 

Steel  (low  carbon) 

2600° 

Steel  (high  carbon)      " 

2400° 

Cast  Iron  (white) 

2200° 

Cast  Iron  (grey) 

2000° 

Copper 

1975° 

Gun  Metal 

I7000 

Zinc 

764° 

Antimony 

940° 

Lead 

618° 

Bismuth 

514° 

Tin 

447° 

Platinum 

3230° 

Gold 

2056° 

Silver 

1788° 

Aluminum 

1172° 

Thermo  =  Electric  Pyrometers  —  When 
wires  of  two  different  metals  are  joined  at 
one  end  and  heated,  an  electromotive  force 
will  be  set  up  between  the  free  ends  of  the 
wires.  Its  amount  depends  upon  the  com- 
position of  the  wires  and  upon  the  temper- 
ature. If  a  delicate  galvanometer  of  high 
resistance  be  connected  to  the  "thermal 
couple",  as  it  is  called,  the  deflection  of 
the  needle,  after  a  careful  calibration,  will 
indicate  the  temperature  very  accurately. 

In  the  thermo-electric  pyrometer  of  Le 
Chatelier,  the  wires  are  platinum  and  a 
10%  alloy  of  platinum  and  rhodium,  en- 
closed in  porcelain  tubes  to  protect  them 
from  the  oxidizing  influence  of  the  furnace 
gases.  The  couple  with  its  protecting  tubes 
is  called  an  "element".  The  elements  are 
made  in  different  lengths  to  suit  conditions. 
It  is  not  necessary  for  accuracy  to  expose 
the  whole  length  of  the  element  to  the  tem- 
perature to  be  measured,  as  the  electro- 
motive force  depends  only  upon  the  tem- 
perature of  the  juncture  at  the  closed  end 
of  the  protecting  tube.  The  galvanometer 
can  be  located  at  any  convenient  point, 
since  the  length  of  the  wires  leading  to  it 
occasions  practically  no  error. 


MEAN   SPECIFIC   HEATS    OF   SOLIDS 


S3 


The  advantages  of  the  thermo-electric 
pyrometer  are:  accuracy  over  a  wide  range 
of  temperature,  continuity  of  readings,  and 
the  ease  with  which  observations  can  be 
taken.  Its  disadvantages  are  high  first 
cost  and  extreme  delicacy. 

Calorimetry — This  method  derives  its 
name  from  that  fact  that  the  process  is  the 
same  as  the  determination  of  the  specific 
heat  of  a  substance  by  the  water  calorimeter, 
with  the  exception  that  in  one  the  temper- 
ature is  known  and  the  specific  heat  is  re- 
quired, while  in  the  other  the  specific  heat 
is  known  and  the  temperature  is  required. 
The  temperature  is  found  as  follows:  A 
given  weight  of  some  substance,  such  as 
iron,  nickle,  platinum,  or  fire-brick,  is  heated 
to  the  unknown  temperature  and  then 
plunged  into  water  and  the  rise  in  temper- 
ature noted. 
If: 

X  =  unknown  temperature  of  substance, 
iv  =  weight  of  heated  substance,  Ibs. 
W  =  weight  of  water,  Ibs. 
T  =  final  temperature  of  water, 
t  =  temperature       rise,      or     difference 
between   initial   and   final   tem- 
peratures of  water, 
s  =  specific  heat  of  cooled  body, 

Wt 

Then:     X=T  +  -  [i] 

ws 


Table  8  gives  the  specific  heats  of  some 
substances  used  in  this  method.  For  furnace 
temperature  determination,  the  constants  in 
the  second  column  should  be  used.  Specific 
heats  increase  with  temperature,  and  author- 
ities differ  as  to  the  amount. 

TABLE  8 
MEAN  SPECIFIC  HEATS 

ORDINARY    MEAN  FOR  HIGH 
SUBSTANCE    TEMPERATURE   TEMPERATURE 


Platinum 
Iron (cast) 
Nickel 
Fire-brick 


.032 
.130 
.  109 
.  200 


.038 
.180 
•136 
.  260 


Example — A  piece  of  wrought  iron  bar, 
weighing  one-half  pound,  is  thrown  into  the 
furnace  and  heated  to  the  temperature  of  the 
fire,  and  is  then  withdrawn  and  placed  in  a 
pail  containing  ten  pounds  of  water.  The 
original  temperature  of  water  was  60°  F.,  and 
after  the  immersion  of  the  iron,  the  tempera- 
ture rose  20°.  The  temperature  of  the  fur- 
nace by  the  formula  was  then  X  =  60  + 
.^ff  =  2282°  F.,  the  specific  heat  of  iron, 
0.18,  being  taken  from  the  table. 

This  method  is  affected  by  many  sources 
of  error,  or  else  requires  so  many  refinements 
of  measurement  that  its  results  are  usually 
very  approximate. 


Air 


Pure  Air  is  a  mixture  of  oxygen  and  nitro- 
gen in  following  proportions:  by  volume  20.91 
parts  oxygen  to  79.09  parts  nitrogen;  by 
weight  23.15  parts  oxygen  to  76.85  parts 
nitrogen.  Air  in  nature  always  contains 
other  constituents  such  as  dust,  carbon 
dioxide,  ammonia,  ozone  and  water  vapor. 

Air  being  perfectly  elastic,  the  density  of 
the  atmosphere  decreases  in  geometrical 
ratio  with  the  altitude.  This  fact  has  an 
important  bearing  on  proportions  of  furnaces 
and  stacks  located  in  high  altitudes,  as  will 
later  appear.  The  atmospheric  pressure 
for  different  altitudes  is  given  in  Table  12*. 

Weight  and  Volume  of  Air — These 
depend  upon  the  pressure  and  temperature, 
as  expressed  in  the  formula 

Pv=53.3T  [2] 

In  which:  P  =  absolute  pressure  in  pounds 
per  square  foot,  v  =  volume  in  cubic  feet  of 
one  pound  of  air,  and  T  =  absolute  temper- 
ature Fah.  of  the  air. 

The  weight  of  one  cubic  foot  of  air  will  be 
evidently  -7  pounds. 

Example:  Required  the  volume  in  cubic 
feet  of  a  pound  of  air  under  60.3  Ibs.  per 
square  inch  gauge  pressure,  at  115°  Fah. 
Here  p  =  144  X  (14.7+  60.3)  =  10,800.  T  -- 
115+461=576,  hence  ^  =  5rf|fip=  2.84  cu. 
ft.  The  weight  per  cubic  foot  will  be  ~?=^ 
=  0.35  Ibs. 

Table  9  gives  weight  and  volume  of  air 
at  different  temperatures. 

The  above  formula  will  hold  good  if  in 
place  of  the  constant  53.3  the  following  con- 
stants be  substituted  for  each  gas  : 

Oxygen  =  48.257 
Nitrogen  =  54.926 
Hydrogen=  770 . 322 

Specific  Heat  of  Air — This  varies  with 
the  temperature.  At  266°  it  is  two  per 
cent.,  and  at  446°  it  is  5.68  per  cent.,  higher 
than  at  32°,  but  the  percentage  of  increase 
for  such  temperatures  as  exist  in  the  boiler 
furnace,  and  along  the  path  of  the  gases 
after  they  leave  the  furnace,  is  not  known. 

Vapor  in  Air — Air  may  carry  as  much  as 
3%  of  vapor.  This  fact  is  of  considerable 


TABLE   9 

VOLUME    AND    WEIGHT    OF    AIR    AT 

VARIOUS  TEMPERATURES,  AND 

ATMOSPHERIC  PRESSURE 


TEMPERATURE 

VOLUME  OF 

WEIGHT  OF 

IN  DEGREES 

ONE  POUND 

ONE  CUBIC 

FAHR. 

CU.  FT. 

FT.  IN  LBS. 

50       .  . 

.  .    I  2.840 

.077884 

55      •  • 

.  .     i  2.964 

•077J33 

60      .  .      .  . 

•  •    i3-°9° 

.076400 

65      ..      .. 

.  .    13.216 

.075667 

70      .  . 

-.    I3-342 

.074950 

75      •  • 

..    13.467 

.074260 

80      .  .      .  . 

••    J3-593 

•073565- 

85      -.      .- 

..    13.718 

.072894 

90      .  . 

•  •    13-845 

.072230 

95      -  • 

•  •    r3-97° 

.071580 

IOO 

.  .    14.096 

.070942 

no 

..    14-346 

.069698 

I  20 

.  .    14-598 

.068500 

130         ..          .. 

.  .    14.849 

.067342 

140 

.  .    15.100 

.066221 

150         .  .          .  . 

••    I5-352 

.065140 

I  60 

..    15.603 

.064088 

170         .  .          .  . 

•  •    I5-854 

.063072 

180      .. 

.  .    16.106 

.062090 

190 

•  •    16.357 

.061134 

200 

.  .    16.606 

.060210 

2IO 

..    16.860 

•°593I3 

212 

.  .    16.910 

•&5d?35 

22O 

.  .    17.111 

.058442 

230 

.  .    17.362 

•057596 

240 

.  .    17.612 

.056774 

250         .  . 

..    17.865 

•055975 

260 

..    18.116 

.055200 

270         ..         .. 

..    18.367 

•054444 

280         .  . 

..    18.621 

•053710 

290 

..    18.870 

.052994 

300 

ig.I  21 

•052297 

320         .  . 

.  .      19.624 

•050959 

340         .  . 

.  .      2O.  I  26 

.049686 

360         .  . 

.  .      20.630 

.048476 

380         ..         .. 

..      21.131 

•047323 

4OO 

.  .      21.634 

.046223 

425         ..          .. 

.  .      22.262 

.044920 

450 

.  .      22.890 

.043686 

475      •  • 

..      23.518 

.042520 

500      .  . 

.  .      24.146 

.041414 

525      -•      •• 

••      24.775 

.040364 

55°     ••      •• 

•  •      25.403 

•039365 

575      ••      •• 

.  .      26.031 

.038415 

600 

.  .     26.659 

•°375Io 

650     .  .      .  . 

•  •      27.913 

.035822 

700 

.  .      29.172 

.034280 

750     ..      .. 

.   .     30.428 

.032865 

importance  in  solving  problems  relating  to 
heating,  drying  and  air  compressing.  Accord- 
ingly Table  10  gives  the  amount  of  vapor 
required  to  saturate  air  at  different  tem- 
peratures, its  weight,  expansive  force,  etc. 


*See  page  58. 


56 


THE    STIRLING   WATER-TUBE    SAFETY    BOILER 


Q 


o 


ffi 

Oi 
CO 

C 


g  ti 

X   ^ 

3g 

Q    O 


^      EH     g 

3      $     § 
M  •-?• 


^      3 


co 


t/ 


s  ^ 

5^    <! 


fa 
O 


fa     PH     CO 

O    S    co 


O 

PH     EH 


<     fa 

H-l 

fa    Q 

co    <! 

EH 

ffl 

O 


Cubic  Feet  of 
Vapor  from  1  Ib. 
of  Water  at  its 

GJ     • 

to   vo   CS    vO    CO         t^»    M 
Qs    CM         vo   vo   O    O     ^"        ^T    to    ^"    M    OO         to    T^-    QN  OO     O        PJ     t^ 
OO     vo        O    to    M     O     ^        to    vo    O    vo    M          O    t~~-    LO    Tt    to        to    O< 

O       d             VO     M     CO     O       ^t"            tO     CS       M       M       M 
tO     CS             MM 

MIXTURES  OF  AIR  SATURATED  WITH  VAPOR. 

Weight  of  Dry 
Air  mixed  with 
1  Ib.  of  Vapor,  in 
Pounds. 

10 

M      VO         t^    O 

M    OO         t^-   O    ^    vo   O        CO     O   vo   O  GO         vo   vo  O     O     HI         vo   O 

Tj"      M       T^-   OO       M             M       t^.     VO     tO     ^            O     O  O       ^J"      Hi              T}*     hH       M       Tt"   CO              tO     O 

d    xO    O     to  OO         cs     Tj*    o    CS     O         M     vo   M    OO    O         ^    to   W     M 
O   "3"    O   O     f^       w   CO     vo  *^*    to       cs     M     M 

Weight  of  Vapor 
mixed  with  1  Ib. 
of  Air,  in  Pounds. 

9 

p»     vo  vo  OM        OOOMO\       r^   PO   ^"    M     O        ^^   to  OO     O     to       O     <U 
O   vo   T^-    t^»  O         M     t^  OO    O    GO         ^"    vo  OO     t^   t^-      O     HI     to    O     "^        to  -*-* 

OOOOO             OMMNPO           TfvOCOMO             PJMVOMP)              O,5 

OOOOO        OOOOO        OOQMM        pjto1^}"   t^  P^       oo   T^ 

M            CM     HH 

Weight  of  Cubic  Foot  of  the  Mixture  of  Air 
and  Vapor. 

Total  Weight  of 
Mixture  in 
Pounds. 
8 

to    M     to    vo  OO          P)     vo    OCMt~—       OOOOOOO          Tj-t^-Oto\O          ^"OO 
\O     *st"    P*     O    OO         t^    vo    to    PI     O        GO     t^-    vo    to    O        GO     vo    PI     O    vo        M    vO 

OOOOO        OOOOO        OOOOO        OOOOO        OO 

Weight  of  the 
Vapor  in  Pounds. 

7 

OOOOO        OOMMP1        pi     to  vo  O   GO        O     to  O     O     vo       O   O 
OOOOO        OOOOO        OOOOO        MMMpjpj        toto 
OOOOO        OOOOO        OOOOO        OOOOO        OO 

Weight  of  the 
Air  in  Pounds. 
6 

\O     "^"    ^     O    GO        VO     ^"    cs     O    CO         *-O   ^O    O^  VO     w         f^*   W    ^O   GO     O         O     O 
CO    CO    CO    GO     f""*        J^**    ^***    r~"*    t^1"  >XO        ^*O    ''O     *^"5    if)   if)        ^"    ""^J"    ^O    C^     C1)          M     O 
OOOOO        OOOOO        OOOOO        OOOOO        OO 

Elastic  Force  of 
the  Air  in  the 
Mixture  of  Air 
and  Vapor  in 
Inches  of 
Mercury. 
5 

GO    GO    OO     t~~  O          vo    to    M    OO     ^3"       OO     M"    to    M     t*—        O  OO     HI     O    O          "^1"    O 

OOOOO        OOOOOOO         f-»    t~-  O     vo    to        M     O    t^>    to    O          vo    O 

PJP4PJCSP4              P)PJP«P)P1             P)P)NP)P«             PJMMMM 

Elastic  Force 
of  Vapor  in 
Inches  of 

Mercury, 
(Regnault). 

4 

nzZS  %z£slzzs~z  IIH1  H 

M       M        M        M             P)        pq 

fjjfjfl  ' 

Tj-piTj-t^M        \OMt^tOO         t^.^P)MO          OCOCOGOO        OM 

OOOOO        OOOOO        OOOOO        OOOOO        OO 

1^1  1 

>Qte 
^ 

"  •*->  Q 

i  rt    i 

•*  O  1~H         M 

56c 

^•>"C 

OOOOO             OOQMM              MMMPJPJ             CSPJPlfOtO           POtO 

~ 
2  ^  H 

OOOOO           OOOOO           OOOOO           OOOOO           OO 
M     PI     to    ^        vo  ^O     r*»  OO     ON        O     M     C^     to    Tf        vo  O     X^»  OO     O        O     M 

Water 


Pure  Water  is  a  chemical  compound  of 
one  volume  of  oxygen  (O)  and  two  of  hy- 
drogen (H),  and  its  chemical  symbol  is  H2O. 

Weight — The  weight  of  water  depends 
upon  its  temperature.  Its  weight  at  four 
temperatures  much  used  in  physical  calcula- 
lations  is  as  follows: 


TEMPERATURE 
FAHRENHEIT 


WEIGHT  PER 
CUBIC   FOOT 


At  32°  or  freezing 

point  at  sea  level  62  .418  Ibs. 
At  39.1°  or  maximum 

density 62  .425 

At  62°  or  standard 

temperature 62.355 

At    212°   or  boiling 

point  at  sea  level    59-760 


WEIGHT  PER 
CUBIC   INCH 

.03612  Ibs. 

.036125  ' 

.03608 

•03458  " 


0.000040  to  0.000051  per  atmosphere,  at 
ordinary  temperatures,  decreasing  however 
with  an  increase  of  temperature. 

Pressure  due  to  Head — The  weight  of 
water  at  standard  temperature  being  62.355 
Ibs.  per  cubic  foot,*  the  pressure  exerted 
by  a  column  of  any  stated  height  may  be 
determined;  and  conversely  the  height  of 
the  column  producing  any  stated  pressure 
can  be  computed. 

Pressure  in  pounds  per  square  foot  « 
62.355  X  height  of  column  in  feet. 

Pressure  in  pounds  per  square  inch  = 
.433  X  height  of  column  in  feet. 

Height  of  column  in  feet  =  Pressure  in 
pounds  per  square  foot  -^62.35  5. 

Height  of  column  in  feet  =  Pressure  in 
pounds  per  square  inch ^-.43 3. 


TABLE    11 


VOLUME   AND  WEIGHT   OF  DISTILLED  WATER   AT 
VARIOUS    TEMPERATURES    (Buet) 


Temper- 
ature 
Fahrenheit 

Relative 
Volume, 

Water  at 
39-1°  =  r 

Weight 
per  Cubic 
Foot. 
Pounds. 

Temper- 
ature 
Fahrenheit 

Relative 
Volume, 
Water  at 
39.1°  =  ! 

Weight 
per  Cubic 
Foot.  . 
Pounds. 

Temper- 
ature 
Fahrenheit 

Relative 
Volume, 
Water  at 
39.1°  =  ! 

Weight 
per  Cubic 
Foot. 
Pounds. 

Temper- 
ature 
Fahrenheit 

Relative 
Volume, 
Water  at 
39-i°  =  i 

Weight 
per  Cubic 
Foot. 
Pounds. 

32° 

I  .  OOOI29 

62  .  42 

1  60° 

I  .02324 

6l  .  OI 

290° 

I  .08405 

57-59 

430° 

I  .  18982 

52-47 

39  -1 

I  .  OOOOOO 

62.43 

170 

I  .  0267  I 

60.80 

3°° 

I  .09023 

57.26 

440 

1.19898 

52.07 

40 

I  .  000004 

62  .42 

1  80 

1.03033 

60.59 

310 

I  .09661 

56-93 

45° 

1.20833 

51.66 

50 

I  .000253 

62  .41 

190 

I  .03411 

60.37 

320. 

1.10323 

56-58 

460 

I  .  21790 

51.26 

60 

I  .  000929 

62.37 

200 

I  .03807 

60.  14 

330 

I  .  IIO05 

56-24 

47° 

I  .  22767 

50.85 

70 

I  .  001981 

62.30 

210 

I  .04226 

59-89 

340 

I  .  11706 

55-88 

480 

1.23766 

5°-44 

80 

I  .00332 

62  .  22 

212 

I  .04312 

59-71 

35° 

1.12431 

55-52 

490 

1.24785 

50.03 

90 

I  .00492 

62  .  12 

22O 

I  .04668 

59-64 

360 

1-13*75 

SS-i6 

5°° 

1.25828 

49.6l 

IOO 

I  .00686 

62  .OO 

230 

1.05142 

59   37 

37° 

1.13042 

54-79 

510 

I  .  26892 

49-20 

no 

I  .  00902 

61.87 

24O 

1-05633 

59-io 

380 

1.14729 

54-4i 

520 

1.27975 

48.79 

I2O 

I.  01143 

61  .  72 

250 

I  .06144 

58-81 

390 

I-I5538 

54-03 

530 

I  .  29080 

48.36 

130 

I  .  0141  1 

61.56 

26O 

I  .06679 

58-52 

400 

I  .  16366 

53-64 

540 

I  -30204 

47-94 

140 

I  .  01690 

61.39 

270 

1.07233 

58-21 

410 

I  .  17218 

53-26 

550 

I-3I354 

47-52 

I  <Q 

I  .  01995 

61  .  20 

280 

I  .07809 

57  .90 

420 

I  .  18090 

52.86 

o 

s  7  \j 

J  1        s 

S 

j 

Compressibility — Water  is  but  slightly 
compressible,  hence  for  all  practical  purposes 
it  may  be  considered  non-compressible. 
The  coefficient  of  compressibility  ranges  from 


Impurities  and  Solvent  Power — Water 
in  its  natural  state  is  never  found  absolutely 
pure.  The  composition  of  feed  water  to  be 
used  for  boilers  is  of  vital  importance,  the 


*Authorities  differ  concerning  the  weight  of  water.     At  62°  F.   the  range  is  from  62.291  to  62.360, 
and  62.355  is  generally  accepted  as  the  most  accurate. 


58 


THE    STIRLING   WATER-TUBE    SAFETY    BOILER 


impurities  existing  in  such  water  affecting 
not  only  the  economy,  but  also  the  durability 
of  the  boiler.  In  solvent  power  water  has 
a  greater  range  than  any  other  liquid.  For 
common  salt  this  is  nearly  constant  at  all 
temperatures,  while  it  increases  with  an  in- 
crease of  temperature  for  such  impurities 
as  magnesium  and  sodium  sulphate. 

Sea  water  contains  on  an  average  about 
3.125  per  cent,  part  of  its  weight  of  solid 
matter,  whose  composition  will  be  approx- 
imately : 

Sodium  Chloride 76% 

Magnesium  Chloride 10 

Magnesium  Sulphate 6 

Calcium  Sulphate  or  Gypsum.     5 

Calcium  Carbonate o£ 

Other  Substances 2\ 

Total 100% 

The  following  are  the  Boiling  Points  and 
Specific  Gravities  of  sea  water  of  varying 
density : 

TAGE  BOILING 

LT  FAHRE1 

2I3 

214 

2IS 

216 

217 
219. 

The  boiling  point  of  water  decreases  as  the 
altitude  above  sea  level  is  increased,  as  shown 
in  Table  12. 

Specific  Heat  of  Water — The  specific 
heat  of  water  is  unity  at  39.1°  F.,  but  for 
other  temperatures  it  is  slightly  greater. 
Rankine  has  constructed  from  Regnault's 
data  the  formula:  Specific  heat  = 

1+0.000000309  (t  -  39.  i)8  [3] 

In  which  t  is  the  temperature  Fah.  In  con- 
sequence of  this  variation  of  specific  heat 
the  heat  of  the  liquid  above  32°  F.  in  any 
case  is  not  exactly  t—  32,  but  is  equal  to  t—  32 
+  o. 000000103 X(t  —  39.  i)3 ,  where  t  is  the 
temperature  of  ebullition.  The  heat  of  the 


liquid  as  computed  for  several  temperatures 
by  both  methods  is  given  below: 


PERCENTAGE 
OF  SALT 
•* 


3 

6 
9 

12 
IS 

18 


125- 
250 

375 
500 
625 

75° 


POINT 

SPECIFIC 

IHEIT 

GRAVITY 

2° 

I  .029 

4° 

1.058 

5° 

1.087 

7° 

i  .  116 

9° 

i-i45 

i° 

1.174 

TEMP.  FAH. 

60 
100 


T-32 

28  B.T.  U. 

68  "  "  " 


RANKINE  S  FORMULA 


28.12  B.  T.  U. 
"  "     "  68.01   "  "     " 

150         118   '  118.30   "  " 

200         168  '  168. 70  "  "     " 

212         180  "  180. 79   "  "     " 

It  will  thus  be  seen  that  the  variation  is 
entirely  too  slight  to  affect  any  but  the  most 
refined  physical  investigations,  and  that  for 
all  steam  engineering  work  the  heat  of  the 
liquid  may  be  safely  taken  as  /  —  32. 

TABLE    12 

BOILING    POINT    OF    WATER    AT 
VARIOUS  ALTITUDES 


Boiling  Point 
in  degrees 
Fahrenheit. 

Altitude  above 
Sea-Level. 
Feet. 

Atmospheric 
Pressure. 
Pounds  per 
square  inch. 

Barometer. 
Inches. 

184 

15,221 

8.19 

16.79 

I85 

14,649 

8-37 

17.16 

186 

14,075 

8.56 

17-54 

187 

I3,498 

8-75 

17-93 

188 

12,934 

8-94 

18.32 

189 

12,367 

9-J3 

18.72 

190 

n,799 

9-33 

*9-*3 

191 

11,243 

9-53 

T9-54 

192 

10,685 

9-74 

19.96 

J93 

10,127 

9-95 

20.39 

194 

9-579 

10.  16 

20.  82 

195 

9,°3! 

10.38 

21.26 

196 

8,481 

10.60 

21.71 

197 

7,932 

10.82 

22.17 

198 

7,38i 

11-05 

22  .  64 

199 

6,843 

11.28 

23.11 

200 

6,304 

11.52 

23-59 

201 

5,764 

II  .76 

24.08 

202 

5-225 

12  .OI 

24.58 

203 

4,697 

12.25 

25.08 

2O4 

4,169 

12.51 

25   59 

2O5 

3,642 

12.77 

26   1  1 

2O6 

3-II5 

I3-03 

26.  64 

207 

2,589 

13.29 

27    18 

208 

2,063 

13-57 

27    73 

2O9 

r>539 

13     84 

28   29 

2IO 

1,025 

14     12 

28  85 

21  I 
212 

512 
Sea-  Lev  el 

14    41 
14     70 

29  42 
30   oo 

*Or  one   thirty-second    part  of  the  weight  of  the   water  and   the  salt  held  in  the  solution. 


Impurities  in  Boiler  Feed  Water 


Natural  waters  usually  contain  other  sub- 
stances in  solution  or  suspension.  When 
the  water  is  converted  into  steam,  these 
substances,  if  solids,  must  be  deposited 
somewhere  in  the  boiler;  if  gases,  they  will 
pass  out  with  the  steam.  The  amount  of 
solids  deposited  in  a  boiler  is  often  aston- 
ishing; over  300  pounds  per  month  will 
deposit  in  a  100  H.  P.  boiler  using  water 
containing  only  7  grains  per  gallon.  In  the 
southwestern  part  of  the  United  States 
where  the  water  is  often  particularly  bad, 
cases  are  known  where  boilers  can  be  operated 
only  two  to  three  days  between  cleanings. 

The  treatment  of  feed  water  belongs  to 
the  chemist  rather  than  to  the  engineer, 
hence  when  the  water  causes  trouble  it  will 
be  economy  to  submit  the  case  to  a  compe- 
tent chemist  who  makes  a  specialty  of  treating 
feed  waters.  His  advice  should  be  followed, 
since  there  are  few  cases  where  guessing 
is  less  successful  than  when  treating  feed 
waters.  The  following  article  is  intended 
to  convey  such  general  information  as  will 
enable  the  reader  to  understand  the  effect 
of  the  impurities  usually  encountered,  and 
to  realize  the  necessity  of  referring  the  more 
difficult  cases  to  an  expert. 

Effect  of  Impurities — According  to  the 
nature  of  the  impurity  it  may  produce  one 
or  several  of  the  following  results: 

(1)  Precipitation  of  mud,  etc. 

(2)  Formation  of  scale. 

(3)  Formation    of    scum    which    causes 
excessive  priming  or  foaming. 

(4)  Internal  corrosion  of  the  boiler. 

Effect  of  Mud  and  Scale — Where  pro- 
vision is  made  to  catch  the  mud  and  blow 
it  off  before  it  settles  on  the  heating  sur- 
face, the  only  evil  effect  is  the  loss  of  heat 
due  to  blowing  off.  If  the  mud  is  carried 
along  and  deposited  on  the  heating  surfaces 
it  may  unite  with  the  scale-forming  matter, 
and  the  mass  will  be  baked  to  a  hardness 
which  renders  its  removal  difficult  and 
costly.  The  arrangement  of  feed  and  mud 
drum  in  the  Stirling  boiler  is  particularly 
efficacious  in  precipitating  mud  and  silt, 
and  the  boiler  is  successfully  operating  on 


waters  which  many  other  types  of  boiler  are 
unable  to  use. 

The  effect  of  scale  depends  largely  upon  its 
density.  The  scale  formed  by  the  carbonates 
is  usually  soft  and  porous,  and  its  retarding 
effect  upon  heat  transmission  is  small,  hence 
unless  present  in  large  quantities  its  influence 
toward  lowering  boiler  efficiency  is  less  than 
commonly  supposed.  Sulphates  and  some 
other  impurities  form  scales  which  are  so  hard 
that  they  can  be  removed  only  by  cutting 
them  loose,  and  so  dense  that  they  are 
impervious  to  water.  Such  scales  are  a 
source  of  positive  danger  which  increases 
with  the  degree  of  temperature  of  the  surface 
upon  which  they  have  formed,  because  the 
metal  overheats  and  is  liable  to  burn,  crack, 
or  bulge,  thereby  causing  a  rupture.  The 
economy  of  the  boiler  is  also  seriously  affected. 
Scale=forming  Materials — Those  which 
occur  most  often  and  in  largest  quantity  are 
Calcium  carbonate  (lime) .  .  .  .CaCO3 

Magnesium  carbonate MgCO3 

Calcium  sulphate CaSO4 

Magnesium  sulphate MgSO4 

The  following  are  less  frequently  found,  and 
usually  in  small  amounts : 

Iron  carbonate Fe2CO3 

Magnesium  chloride MgCl2 

Calcium  chloride CaCl2 

Potassium  chloride KC1 

Sodium  chloride NaCl 

and,  variously,  iron  oxide  and  hydroxide, 
calcium  phosphate,  silica,  and  organic  matter.  • 
The  carbonates  of  calcium  and  magnesium 
are  but  slightly  soluble  in  water;  they  are 
usually  combined  with  carbon  dioxide  as 
bicarbonates,CaH2  (CO3)2  andMgH2  (CO3)2 
respectively,  which  are  quite  soluble  in  cold 
water.  Heating  the  water  drives  off  the 
carbon  doxide,  CO2,  and  the  bicarbonates 
decompose,  precipitating,  in  the  case  of  cal- 
cium the  monocarbonate,  CaCO3 ,  and  mag- 
nesium hydrate,  Mg(OH)2,  in  the  case  of 
magnesium.  This  occurs  between  the  tem- 
peratures 1 80°  to  290°  F.  As  the  scale 
formed  by  calcium  carbonate  is  porous  and 
does  not  adhere  strongly  to  the  metal,  it  is 
not  particularly  troublesome  unless  present 


60 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


in  large  quantity.  The  same  is  true  of  mag- 
nesium carbonate,  but  in  the  process  of  free- 
ing the  carbon  dioxide,  CO2,  the  bicarbonate 
generally  reduces  to  magnesium  hydrate, 
Mg  (OH)»,  which  not  only  follows  the  water 
currents  and  settles  very  slowly,  but  it 
cements  together  such  other  matter  as  it 
may  encounter.  The  violent  foaming  which 
is  often  caused  by  carbonates  of  calcium  and 
magnesium  may  cause  far  more  trouble  than 
the  scale  produced  by  these  salts. 

The  sulphates  of  calcium  and  magnesium 
are  the  most  troublesome  scale-forming 
impurities.  They  remain  in  solution  until 
a  temperature  of  about  302°  is  reached,  when 


selves.  They  may,  however,  cause  foaming, 
which  will  be  greater  as  the  solution  becomes 
more  concentrated.  Frequent  blowing  off 
prevents  their  concentration,  but  wastes  heat 
carried  off  by  the  hot  water. 

A  temperature  of  302°  F.  corresponds  to 
55  Ibs.  gauge  pressure,  hence  the  reason 
why  the  rear  bank  of  the  Stirling  boiler 
removes  most  of  the  scale-forming  matter 
before  the  hotter  parts  of  the  boiler  are 
reached  is  now  evident.  The  water  upon 
entering  the  feed  drum  is  heated  to  the 
temperature  corresponding  to  the  boiler 
pressure,  hence  during  its  course  through 
the  rear  tubes  the  scale  will  be  deposited 


TABLE    13 
SOLUBILITIES   OF   SCALE-FORMING   MINERALS 


' 

SOLUBLE   IN 
PARTS  OF   PURE 
WATER   AT 

32°  F. 

SOLUBLE  IN 
PARTS   OF   CAR- 
BONATED 
WATER,   COLD. 

SOLUBLE   IN 
PARTS  OF  PURE 
WATER  AT   212° 

INSOLUBLE  IN 
WATER  AT 

Calcium  Carbonate 
Calcium  Sulphate  .... 
Magnesium  Carbonate 
Calcium  Phosphate 
Oxide  of  Iron          .... 

62,500 

500 

5.500 

ISO 

'5° 
1.333 

62,500 
460 
9,6OO 

302°  F. 
302°  F. 

212°  F. 
212°  F. 

Silica 

212°   F. 

the  calcium  sulphate  deposits  in  long,  needle- 
like  crystals,  possessing  active  cementing  prop- 
erties. These  mingle  with  any  other  matter 
present  to  form  a  hard  resisting  scale.  The 
^agnesium  sulphate  will  deposit  as  a  mono- 
hydrated  salt,  MgSO4H2O,  and  its  presence 
is  objectionable  because  it  interferes  with  the 
removal  of  other  impurities. 

The  iron  carbonate  behaves  much  like 
calcium  monocarbonate,  CaCO3  ,but  it  occurs 
so  seldom  and  in  such  small  quantities  that 
its  presence  has  little  effect. 

The  magnesium  chloride  precipitates  as  a 
hydroxide,  which  is  objectionable  because 
of  its  cementing  properties.  The  other  chlor- 
ides, calcium,  potassium  and  sodium  (com- 
mon salt) ,  give  little  trouble  from  incrustation 
unless  allowed  to  concentrate  beyond  the 
point  of  saturation,  when  they  are  deposited 
and  increase  the  bulk  of  the  scale,  although 
possessing  no  cementing  properties  them- 


and  the  purified  water  will  pass  into  the  hot- 
test tubes  in  the  front  bank.  This  feature 
is  peculiar  to  the  Stirling  boiler.  Here  also, 
as  in  case  of  feed  water  heaters,  the  element 
of  time  affects  the  degree  to  which  the  im- 
purities can  be  removed,  hence  it  is  evident 
that  the  more  the  boiler  is  forced,  the  shorter 
the  time  the  water  can  remain  in  the  rear 
bank,  hence  the  smaller  the  degree  to  which 
this  water  can  be  purified  before  passing 
into  the  front  and  middle  banks. 

Scum  may  be  due  to  vegetable  matter, 
sewage,  and  light  flocculent  matter  which 
gathers  on  top  of  the  water.  These  form 
a  glutinous  skin  on  the  water,  which  is 
raised  by  the  steam,  causing  foaming  or 
priming  which  may  be  so  excessive  as  se- 
riously to  interfere  with  operation  of  the 
engines.  When  animal  and  vegetable  oils 
are  used  as  components  of  the  cylinder  oil, 
and  the  hot-well  water  containing  them 


HOW   TO    HANDLE    IMPURE    FEED    WATER 


61 


is  mixed  with  feed  water  containing  soda, 
the  oils  are  saponified,  soap  suds  are  formed, 
and  violent  foaming  may  result.  The  remedy 
is  to  use  mineral  oil.  The  scums  are  best 
handled  by  a  surface  blow-off. 

Pitting  and  Corrosion  are  usually  caused 
by  free  acids  which  are  either  originally 
in  the  water  or  are  liberated  by  splitting 
up  some  salt.  The  acids  may  be  of  vegetable 
origin  derived  from  some  adulterant  of 
mineral  oil,  or  the  original  water  may  have 
been  polluted  with  acid  due  to  discharge 
from  industrial  works,  or  drainage  from 
mines;  waters  from  swamps  and  bogs  often 
contain  humic  or  vegetable  acids;  sulphuric 
acid  is  often  absorbed  from  the  atmosphere, 
and  found  in  drainage  from  coal  and  ore 
mines,  particularly  if  the  ores  are  sulphides. 

Magnesium  chloride  is  generally  thought 
to  have  a  corrosive  effect  on  boiler  plate. 
Some  assert  that  it  is  broken  up  by  the  boiling 
water  into  magnesium  hydrate  and  hydro- 
chloric acid ;  while  others  notably  H .  Ost ,  main- 
tain that  water  is  partly  decomposed  by  boil- 
ing, and  the  iron  of  the  boiler  is  attacked  by 
liberated  oxygen,  the  magnesium  chloride 
subsequently  combining  with  the  iron  pro- 
toxide thus  formed;  the  reaction  being  as 
follows : 

MgCl,+Fe(OH)2  =  FeCl2  +  Mg(OH)2 

If  Ost's  theory  is  correct,  corrosion  takes 
place  quite  independently  of  the  magne- 
sium chloride. 

Air  absorbed  by  water  is  liberated  by 
boiling,  and  produces  corrosion.  The  pe- 
culiar activity  of  air  under  such  circum- 
stances is  due  to  the  fact  that  whereas  or- 
dinary air  is  a  mixture  of  oxygen  and  nitrogen 
in  the  approximate  ratio  of  i  to  4,  airr'-ssolved 
in  water  is  a  mixture  of  i  part  of  oxygen 
and  only  1.87  parts  of  nitrogen,  owing  to 
the  greater  solubility  of  oxygen.  The  deter- 
rent-effect of  nitrogen  as  a  dilutant  is  thus  re- 
duced, and  the  mixture  is  correspondingly 
more  active  chemically.  In  the  experiments 
of  Lt.  Comdr.  W.  F.  Worthington,  U.  S.  N., 
samples  of  iron  and  steel  were  supported 
on  glass  rolls  in  a  porcelain  bath  of  distilled 
water  through  which  air  was  forced.  The 
corrosion  of  the  iron  and  steel  was  marked, 
in  some  cases  occurring  uniformly  over 
the  surface  of  the  samples,  and  in  other 
cases  being  confined  to  pits  of  small  area, 


but  of  surprising  depth.  The  temperature 
at  which  the  oxygen  most  rapidly  attacks 
the  iron  is  lower  than  that  of  steam  at  the 
pressures  now  used,  hence  it  will  be  found 
that  pitting  will  occur  much  faster  in  a 
boiler  that  is  moderately  warm  than  when 
in  full  service;  it  also  occurs  in  places  where 
the  circulation  is  defective,  such  as  in  water- 
legs.  The  rapid  corrosion  of  feed  pipes  is 
similarly  explained — the  temperature  falls 
within  the  range  in  which  oxygen  rapidly 
attacks  the  iron. 

When  water  contains  alkali,  any  copper 
used  in  the  boiler  will  rapidly  pit  and  corrode 
in  parts  where  the  circulation  is  defective. 
The  oxygen  attacks  the  copper  and  the  alkali 
dissolves  the  copper  oxide  so  formed,  thus 
presenting  a  fresh  surface  to  the  action  of 
the  oxygen.  With  such  waters  copper  fire- 
box plates  one-half  inch  thick  have  been 
pitted  through  in  five  months. 

How  to  Handle  Impure  Feed  Water — 
There  are  three  courses  of  procedure,  viz.: 

(1)  To  neutralize  the  acids  and  remove 
the  solids  before  the  water  enters  the  boiler. 

(2)  To   treat   the   water   with    chemicals 
after  it  has  entered  the  boiler,  with  a'  view 
of    minimizing    or    preventing    formation    of 
incrustation  and  scale. 

(3)  To  evaporate  the  water  and  remove  at 
regular   intervals   the    deposits   which    form. 

Unless  the  water  is  of  very  good  quality 
the  first  course  is  preferable,  and  the  most 
economical  in  the  end.  The  design  of  the 
equipment  for  efficient  treatment  will  depend 
upon  the  character  of  the  impurities  in  the 
water,  and  the  work  should  be  entrusted  only 
to  an  expert.  The  necessary  equipment  is 
generally  too  expensive  to  be  provided  for 
small  steam  plants,  and  recourse  must  be 
had  to  the  other  methods. 

Free  acids  should  receive  attention  before 
the  water  enters  the  boiler  or  heater.  While 
milk  of  lime  fed  into  the  boiler  will  form 
a  thin  coating  which  to  some  extent  prevents 
the  acid  from  corroding  the  metal,  the  proper 
procedure  is  to  neutralize  the  acid  before 
the  water  is  used.  If  free  acid  only  is  present, 
it  may  be  neutralized  by  addition  of  carbonate 
of  soda,  but  an  excess  of  the  carbonate 
may  cause  considerable  priming.  If  scale- 
forming  materials  are  present  with  the  acid, 
more  elaborate  processes  will  be  necessary. 


REMOVAL   OF   SCALE   FROM    BOILERS 


63 


If  the  water  is  suspected  of  containing  acid, 
it  should  be  tested  by  inserting  blue  litmus 
paper,  which  will  turn  red  if  acid  is  present. 
The  water  should  then  be  submitted  to  a 
chemist,  and  the  quantity  of  bicarbonate 
of  soda  required,  or  the  necessity  for  more 
elaborate  treatment,  should  be  determined 
and  prescribed  by  him. 

Heating  Feed  Water  not  only  saves  heat, 
but  serves  as  a  means  of  external  purification 
more  or  less  efficient  according  to  the  kind  of 
impurities  present.  At  the  temperature  of 
208°  to  210°  attainable  in  open  or  closed  heat- 
ers some  of  the  carbonates  and  other  impuri- 
ties can  be  precipitated.  Since  sulphate  of 
lime  precipitates  at  302°,  corresponding  to  55 
Ibs.  pressure,  a  live  steam  heater  will  remove 
most  of  it,  if  it  be  of  sufficient  size  and  kept 
clean.  The  element  of  time  has  considerable 
effect  in  precipitating  impurities,  hence  the 
results  will  be  better  when  both  open  and 
closed  heaters  are  of  sufficient  size  to  allow 
the  water  to  remain  a  considerable  time  under 
influence  of  the  heat. 

Treatment  after  Water  Enters  the 
B o  i  1  er — The  ob j ect  of  such  treatment  is  to  con- 
vert the  scale-forming  impurities  into  others 
which  are  less  objectionable.  This  method 
affords  a  fertile  field  to  the  vendor  of  "com- 
pounds." When  prepared  by  a  chemist  for  a. 
particular  water,  such  preparations  may  be  of 
great  benefit,  but  their  use  without  adequate 
knowledge  of  what  they  contain  and  the 
effect  of  the  ingredients  on  the  impurities 
of  the  water,  can  be  compared  only  with  the 
use  of  "cure-alls"  in  medicine.  When  im- 
properly used  they  produce  quite  as  much 
trouble  as  the  impurities  they  are  expected 
to  neutralize.  Even  when  properly  com- 
pounded their  office  is  to  convert  a  certain 
amount  of  objectionable  solids  into  a  greater 
amount  of  less  objectionable  solids.  If  they 
fail  they  have  only  increased  the  evil  they 
were  expected  to  cure,  hence  the  necessity 
of  consulting  a  chemist  when  compounds  are 
to  be  used. 

The  Reagents  used  to  Neutralize  the 
Principal  Impurities  will  now  be  given. 

Calcium  and  magnesium  carbonates  are 
precipitated  to  some  extent  by  heat,  because 
the  carbon  dioxide,  CO 2,  necessary  to  hold 
them  in  solution  is  driven  off.  They  may 
also  be  precipitated  by  caustic  lime  CaOHa 


which  reduces  them  to  the  practically 
insoluble  carbonates.  Sodium  hydroxide  or 
caustic  soda,  NaOH,  accomplishes  the  sams 
result. 

Magnesium  and  calcium  sulphates  and 
chlorides  are  convertible  into  carbonates  by 
the  use  of  soda-ash,  Na2CO3.  As  carbon- 
ates, they  are  merely  lesser  evils  than  when 
sulphates.  The  resulting  sodium  sulphate 
or  chloride,  is  harmless,  requiring  only  oc- 
casional blowing  off  to  prevent  it  from  con- 
centrating. 

If  the  use  of  a  solvent  is  necessary,  there  is 
in  most  plants  no  way  of  getting  it  into  the 
boilers  without  shutting  them  down  and 
introducing  it  through  the  manhole.  If  this 
is  done  only  when  the  boilers  are  opened  for 
cleaning  no  extra  expense  is  involved,  but, 
as  a  rule,  the  stoppages  are  so  far  apart  that 
the  introduction  of  the  solvent  accomplishes 
little,  because  in  the  natural  course  of  run- 
ning it  will  be  blown  out  long  before  the  next 
charge  is  introduced.  Small  quantities  of 
solution  introduced  at  short  intervals  are 
more  effective  than  a  large  quantity  at  longer 
intervals,  and  when  the  water  is  very  bad 
a  much  greater  quantity  of  the  solvent  can 
be  used  in  a  given  time  than  is  possible  where 
large  quantities  are  introduced  at  long 
intervals.  With  some  waters  a  charge  of 
30  pounds  of  soda-ash  once  a  month  might 
cause  serious  priming  immediately  after  being 
introduced,  while  one  pound  a  day  could 
have  no  evil  effect. 

The  proper  way  to  introduce  the  solvent  is 
to  attach  to  the  feed  pump  suction  an  appa- 
ratus arranged  to  feed  it  just  as  cylinder  oil  is 
fed  to  an  engine.  There  are  many  inex- 
pensive appliances  of  this  kind  on  the  market ; 
a  satisfactory  home-made  appliance  consists 
of  a  tee  in  the  suction  pipe,  with  a  gate  valve 
on  the  hot- well  side  of  it,  the  outlet  of  the 
tee  being  turned  upward,  and  connected 
to  a  nipple  which  in  turn  is  connected  to  a 
vessel  containing  the  solution.  A  valve  is 
also  placed  in  the  nipple.  By  opening  this 
valve  and  closing  the  valve  in  suction  pipe, 
the  solution  is  drawn  into  the  pump  and 
passed  to  the  boiler.  The  action  must  be 
intermittent,  and  is  not  so  efficient  as  when 
a  continuous  feed  in  small  quantity  is  used. 

Removal  of  Scale — Even  with  a  system 
of  purification  it  is  practically  impossible  to 


64 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


get  the  water  absolutely  pure,  hence  some 
deposit  will  form  in  course  of  time  Without 
purification  this  deposit  will  form  more  or 
less  rapidly  according  to  character  of  the 
water,  and  its  removal  is  essential  to  effi- 
ciency and  durability  of  the  boiler.  The  most 
efficient  appliance  for  this  work  is  a  turbine 
tube  cleaner,  the  construction  of  which  is  de- 
scribed in  the  chapter  on  Boiler  Cleaning. 


of  |-inch  thickness  will  raise  the  temperature 
of  the  furnace  plates  about  300  degrees 
Fahrenheit.  As  grease  offers  ten  times  more 
resistance  to  heat,  one  would  expect  that  .0125 
inch  would  have  the  same  effect  as  this 
thickness  of  scale,  but  experience  shows  that 
the  merest  trace  of  grease,  certainly  less 
than  o.ooi  inch,  or  one-tenth  of  the  above, 
can  cause  far  more  injury  than  scale."* 


4,000    H.  P.  OF  STIRLING   BOILERS,  GUANICA   CENTRALE,  PUERTO   RICO 


Extraction  of  Oil  and  Grease  from  Feed 
Water — If  feed  water  is  taken  from  a  hot- 
well  the  cylinder  oil  should  be  removed 
from  it  before  it  enters  the  boiler.  In  some 
districts  where  oil  wells  are  common,  much 
of  the  water  available  for  boiler  feed  contains 
native  oil.  If  this  is  allowed  to  enter  the 
boilers,  it  will  deposit  on  the  hot  surfaces,  and 
these  will  inevitably  be  burned  or  blistered. 
The  oil  is  also  liable  to  cause  heavy  priming. 
"The  peculiarity  of  grease  deposits  in  boilers 
is  that  their  effect  is  out  of  all  proportion  to 
their  thicknesses.  We  have  seen  that  scale 


Where  the  cylinder  oil  forms  an  emulsion 
with  the  hot- well  water  its  removal  is  difficult, 
if  not  impossible,  and  the  remedy  is  to  select 
an  oil  which  will  not  produce  such  emulsion. 
An  oil  extractor  should  be  placed  on  the 
exhaust  pipe,  but  while  this,  if  properly 
looked  after,  will  remove  a  considerable 
portion  of  the  oil,  the  amount  which  passes 
through  it  is  too  great  to  be  allowed  to  enter 
the  boiler.  Various  devices  are  employed 
to  extract  the  remainder  of  this  oil.  If  an 
open  heater  is  used  it  should  be  provided 
with  an  oil  extracting  device  of  liberal 


*Sec  Water-Softening,  by  C.   E.  Stromeyer  and  W.  B.   Baron.     Engineering,  London,  Dec.  25,  1903. 


CLASSIFICATION    OF   FEED    WATERS 


65 


capacity.  In  some  cases  the  water  from  con- 
denser or  open  heater  is  made  to  flow  into 
a  large  box  divided  into  compartments 
by  vertical  partitions,  the  water  passing 
over  one  partition,  then  under  the  next,  then 
over  the  third,  etc.,  until  it  reaches  the 
final  compartment  from  which  it  is  drawn 
by  the  feed  pump.  In  each  compartment 
is  placed  a  basket  made  of  wire  netting,  and 
loosely  packed  with  hay,  excelsior,  etc., 
through  which  the  water  must  pass.  Each 
basket  can  be  removed  independently,  and 
be  charged  with  fresh  filtering  material. 
Each  compartment  is  provided  with  surface 
and  bottom  blow-off.  Another  method  is 


When  oil  has  been  allowed  to  enter  the 
boiler  it  should  at  once  be  removed  in  the 
manner  prescribed  on  page  228, 

Good  and  Bad  Feed  Water — It  is  diffi- 
cult to  judge  of  the  quality  of  a  feed  water 
by  the  number  of  grains  of  solids  per  gallon, 
for  the  reason  that  whereas  50  grains  of  some 
soluble  salt,  such  as  sodium  chloride,  might 
be  handled  with  success,  only  8  grains  of 
calcium  sulphate  might  render  the  water 
unsuitable  for  boilers.  The  following  clas- 
sification rates  waters  according  to  the  num- 
ber of  grains  of  incrusting  solids  (calcium 
carbonate,  magnesium  carbonate,  magnesium 
chloride,  etc.)  per  gallon. 


TABLE   14 
EFFECT  OF,  AND  CORRECTIVES  FOR,  IMPURITIES  IN   FEED  WATER    (Norton} 


TROUBLESOME    SUBSTANCE. 


TROUBLE. 


REMEDY    OR    PALLIATION. 


Sediment,  mud,  clay,  etc.       .     .     . 

Readily  soluble  salts 

Bicarbonates  of  lime,  magnesia,  iron 


Sulphate^of  lime 


Chloride  and  sulphate  of  magnesium 
Carbonate  of  soda  in  large  amounts 

Acid 

Dissolved  carbonic  acid  and  oxygen 

Grease  (from  condensed  water) 
Organic  matter  (sewage)  .... 
Organic  matter 


Incrustation. 
Incrustation. 
Incrustation. 

Incrustation. 

Corrosion. 
Priming.  % 
Corrosion. 
Corrosion. 

Corrosion. 

Priming. 

Corrosion. 


Filtration.       Blowing  off. 

Blowing  off. 

Heating    feed.     Addition    of    caustic 

soda,  lime,  or  magnesia,  etc. 
Addition  of  carbonate  of  soda,  barium 

chloride. 

Addition  of  carbonate  of  soda. 
Addition  of  barium  chloride. 
Alkali. 
Heating    feed.     Addition    of    caustic 

soda  or  slacked  lime. 
Slacked  lime  and  filtering.      Carbonate 

of  soda.     Substitute  mineral  oil. 
Precipitate  with  alum  or  ferric  chloride 

and  filter. 
Precipitate  with  alum  or  ferric  chloride 

and  filter. 


to  insert  into  the  feed  pipe  between  the  pump 
and  the  boiler  two  receptacles  so  piped  that 
the  water  can  be  pumped  through  either 
of  them  while  the  other  is  being  cleaned; 
these  are  arranged  so  that  the  water  has 
to  pass  through  layers  of  sponges,  burlap, 
or  other  filtering  material,  which  can  easily 
be  renewed.  Whatever  arrangement  be  a- 
dopted,  it  is  necessary  to  renew  the  filtering 
material  at  regular  intervals,  and  to  ascertain 
by  frequent  inspection  of  the  boiler  that 
practically  all  the  oil  is  removed  from  the 
feed  water. 


Less  than  8  grains*. . 
From  8  to  1 2      "      ... 

12  to  15    '       ... 

15  to  20    " 

20  to  30 


.  Very  good 

.Good 

.Fair 

.Poor 

.Bad§ 


Greater  than  30  grains. .  .  .  Very  bad 
Much  smaller  quantities  of  sulphates  of 
calcium  (lime)  and  magnesium  will  bring 
the  quality  of  water  lower  down  in  the  scale. 
For  a  rough  comparison  it  may  be  said  that 
one  grain  of  these  solids  would  be  as  harmful 
as  two  to  three  grains  of  the  carbonates  and 
chlorides  above  mentioned. 


*One  pound  avoirdupois  =  7,000  grains.      ^Similar  result  is    caused    by    carbonates   of    calcium    and 
magnesium.      $Such  water  should  not  be  used  in  a  boiler  unless  first  purified. 


The  Heating  of  Boiler  Feed  Water 


Before  the  water  fed  into  a  boiler  can  be 
converted  into  steam  it  must  be  heated  from 
its  original  temperature  to  that  corresponding 
to  the  steam  pressure.  Steam  at  160  Ibs. 
gauge  pressure  has  a  temperature  of  about 
370°  Fahr.,  hence  if  the  feed  should  be  at  a 
temperature  of  60  degrees  each  pound  of  this 
water  must  absorb  about  310  B.  T.  U.  be- 
fore it  can  be  converted  into  steam.  This 
amount  of  heat  is  nearly  27%  of  the  total 
heat  needed.  Obviously,  then,  if  before  the 
water  is  pumped  into  the  boiler  it  can  be 
made  to  absorb  heat  which  otherwise  would 
go  to  waste  through  the  engine  exhaust,  or 
the  flue-gases,  it  will  be  economy  to  save 
this  heat,  provided  the  cost  of  doing  so  is 
less  than  the  value  of  the  heat  which  is  saved. 

The  steam  pressure  and  feed  water  tem- 
peratures before  and  after  heating  being 
known,  the  fuel  saving  can  be  computed  by 
the  following  formula: 

100  (/— /, ) 


Fuel  saving  in  per  cent.  - 


[4] 


in  which  t  =  temperature  Fahr.  of  feed  water 
after  heating,  tl  =temperature  Fahr.  of  feed 
water  before  heating,  and  //-total  B.  T.  U. 
above  32°  Fahr.  per.  pound  of  steam  at  the 
boiler  pressure  from  Table  18,  page  74. 

To  effect  this  saving,  money  must  be  ex- 
pended for  feed  heating  apparatus,  piping, 
space  in  which  to  install  them,  and  labor 
to  operate  them.  The  heating  may  be  done 
by  use  of  exhaust  steam  heaters,  of  either  the 
open  or  closed  type,  according  to  character 
of  the  feed  water,  and  nature  of  the  plant; 
or  by  economizers,  or  by  a  combination  of  the 
two  systems.  Which  of  these  to  choose  can 
be  determined  only  after  a  study  of  the  con- 
ditions in  each  case.  For  example,  if  the 
exhaust  steam  can  all  be  used  for  heating, 
drying,  ice-making,  etc.,  its  value  when  so 
utilized  may  exceed  its  value  as  a  feed  heat- 
ing medium,  and  an  economizer  should  be 
considered.  If  the  exhaust  steam  cannot  be 
thus  utilized,  an  open  or  closed  heater  can  be 
considered,  and  here  again  the  wisest  selection 
can  be  made  only  after  study  of  the  conditions. 
When  using  certain  feed  waters  heavily  im- 
pregnated with  mineral  a  closed  heater  may 


scale  up  so  rapidly  that  its  efficiency  quickly 
falls  off,  and  its  cost  of  cleaning  may  be  pro- 
hibitive, hence  for  such  waters  an  open 
heater  should  be  preferred.  When  engines 
work  intermittently,  as  a  mine  hoist,  a  closed 
heater  is  not  advisable,  because  the  frequent 
coolings  between  hoists  and  the  sudden  heat- 
ing when  each  lift  begins  will  soon  loosen 
the  tubes,  or  even  pull  them  apart,  hence 
an  open  heater  or  an  economizer  will  give 
more  satisfactory  service 

Economizers  are  bulky,  require  a  large 
amount  of  extra  brickwork  or  an  expensive 
metal  housing,  and  frequently  a  considerable 
increase  in  the  space  necessary  for  heaters 
of  the  exhaust  steam  type.  When  comput- 
ing the  net  return  on  an  economizer  invest- 
ment, all  these  factors  must  be  included. 
When  the  feed  water  is  of  a  character  that 
will  quickly  scale  or  incrust  the  economizer, 
and  throw  it  out  of  service  for  cleaning 
during  an  excessive  proportion  of  time, 
consideration  must  be  given  to  the  problem 
of  purifying  the  water  before  it  passes  to  the 
economizer,  or  the  latter  may  fail  to  earn  a 
profit  on  the  investment.  The  character  of 
fuel  and  type  of  boiler  used  also  have  more  in- 
fluence on  the  economizer  problem  than  com- 
monly supposed.  The  more  wasteful  the  boiler, 
the  greater  the  saving  by  using  an  economizer. 
When  oil  fuel  is  used  under  a  large  boiler  of 
efficient  design,  the  boiler  efficiency  may 
and  often  does  exceed  80  per  cent.,  thus 
leaving  small  opportunity  for  an  economizer, 
and  there  are  cases  where  economizers  have 
been  a  source  of  profit  while  the  boilers  were 
fired  with  coal,  but  the  net  saving  disappeared 
as  soon  as  oil  fuel  was  used,  and  the  same 
would  be  the  case  with  gas  fuel. 

From  the  foregoing  it  is  evident  that  general 
data  as  to  the  saving  that  can  be  effected  by 
heating  feed  water,  or  detailed  computations 
based  on  assumed  conditions,  can  be  of  little 
practical  use.  Each  case  must  be  independ- 
ently worked  out,  which  can  be  done  in- 
telligently only  after  exhaustive  study  of 
each  of  the  conditions  affecting  that  case, 
including  probable  life  and  growth  of  the 
plant.  When  as  a  result  of  such  a  study 


68 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


the  different  methods  practicable  for  hand- 
ling the  problem  have  been  determined,  the 
selection  of  the  best  one  can  be  easily  deter- 
mined by  balancing  the  saving  possible 
with  each  method  against  its  first  cost,  depre- 
ciation, maintenance,  and  cost  of  operation. 


the  advantage  of  the  boiler;  the  capacity  of 
the  boiler  is  increased  by  the  amount  of  heat 
added  to  the  feed,  and  the  stresses  caused  by 
feeding  cold  water  into  the  boiler  are  reduced. 
Introduction  of  cold  water  into  a  boiler  is 
also  an  occasional  cause  of  priming.  For 


BULL   RIVETERS    IN    $RUM    SHOP   OP   THE   STIRLING    COMPANY'S   WORKS 


Thus  far,  only  fuel  saving  has  been  con- 
sidered. But  beside  this,  the  benefits  of 
heating  feed  water  are  many.  The  proper 
office  of  a  boiler  is  to  generate  steam,  and  to 
do  this  most  profitably  it  requires  to  be  kept 
clean.  By  properly  heating  the  feed  water, 
most  of  the  impurities  can  be  eliminated  to 


these  reasons,  heating  of  feed  water  is  common 
even  when  fuel  saving  is  not  the  main  object, 
as  in  saw  mills  and  in  cases  where  feed  water 
purification  is  necessary,  as  exemplified  in 
the  use  of  live  steam  heaters  which  purify, 
but  considered  as  heaters  only,  save  little  or 
no  fuel. 


Steam 


Gases  and  Vapors — If  the  temperature 
of  a  gas  be  kept  constant  its  pressure  may  be 
increased  by  making  a  corresponding  decrease 
in  its  volume.  Vapors,  which  are  simply  liquids 
converted  into  aeriform  condition,  can  exist 
only  in  connection  with  a  definite  pressure 
corresponding  to  each  temperature.  Thus 
water  vapor,  or  steam,  of  150  pounds  per  sq. 
inch  absolute  pressure,  can  exist  only  under 
a  temperature  of  about  358°  F.;  hence  if  the 
pressure  of  saturated  steam  be  fixed  its 
temperature  also  becomes  fixed,  and  vice 
versa. 

Saturated  Steam  is  steam  which  is  at  the 
maximum  pressure  and  density  possible  at 
its  temperature,  or  is  steam  in  the  condition 
in  which  it  is  generated  from  water  with 
which  it  is  in  contact.  If  either  the  pressure 
be  increased,  or  the  temperature  be  decreased, 
some  of  the  steam  will  immediately  condense. 
Just  so  long  as  steam  is  of  the  same  pressure 
and  temperature  as  the  water  with  which  it 
can  remain  in  contact  without  gaining  or 
losing  heat,  it  will  remain  saturated. 

Quality  of  Steam — Dry  saturated  steam 
contains  no  water.  In  all  practical  cases 
saturated  steam  contains  some  water,  which 
is  suspended -in  it,  and  the  steam  is  then  said 
to  be  wet.  The  percentage  weight  of  the 
steam,  in  a  mixture  of  steam  and  water,  is 
called  the  quality  of  the  steam.  Thus  if  it  be 
found  that  for  each  100  pounds  of  the  mixture 
there  is  f -pound  of  water  the  quality  of  steam 
will  be  99.25. 

Superheated  Steam — If  heat  be  added  to 
steam  out  of  contact  with  water,  both  tem- 
perature and  pressure  increase,  provided  the 
volume  remains  constant,  or  the  temperature 
and  volume  increase  if  the  pressure  remains 
constant.  Steam  whose  temperature  exceeds 
that  of  saturated  steam  of  the  same  pressure 
is  called  superheated  steam  and  its  properties 
approximate  those  of  a  perfect  gas. 

Heat  of  the  Liquid,  Latent  Heat,  and 
Total  Heat  of  Steam — As  explained  in 
the  chapter  on  Heat,  the  heat  necessary 
to  raise  the  water  from  32°  F.  to  point  of 
ebullition  is  called  heat  of  the  liquid.  The 
heat  absorbed  during  the  ebullition  consists 


of  that  necessary  to  dissociate  the  molecules, 
or  the  inner  latent  heat;  and  that  necessary 
to  overcome  the  resistance  to  increase  in 
volume,  or  the  outer  latent  heat,  and  these 
two  are  the  total  latent  heat  of  vaporization, 
as  given  in  the  Steam  Tables,  page  74. 

Relative  Volume — The  relative  volume 
of  steam  is  the  ratio  between  the  volumes 
of  an  equal  weight  of  steam,  and  of  water 
at  39.1°  F.,  and  it  is  equal  to  the  volume 
in  cubic  feet  of  one  pound  of  steam  multiplied 
by  62.425.  Example:  A  pound  of  steam 
at  250°  F.  occupies  a  volume  of  13.65  cubic 
feet,  hence  its  relative  volume  is 
13.65X62.425=852.1. 

The  Specific  Volume  of  saturated  steam 
is  the  volume  in  cubic  feet  of  one  pound 
of  steam. 

Boiling  Point — The  temperature  of  the 
boiling  point  of  any  liquid  depends  upon 
the  pressure  on  the  liquid.  This  fact  is  of 
great  practical  importance  in  steam  con- 
densers, and  in  many  operations  requiring 
boiling  in  an  open  vessel,  since  in  the  latter 
case  altitude  has  considerable  influence. 
The  relation  between  altitude  and  boiling 
point  is  shown  in  Table  12,  page  58. 

Equivalent  Evaporation  from  and  at 
212°  F. — When  comparing  boiler  tests, 
fuel  performances,  etc.,  it  is  usually  found 
that  neither  the  steam  pressure  nor  the 
feed  water  temperature  was  the  same  in 
the  various  trials,  hence  it  is  necessary  to 
establish  some  common  basis  to  which  all 
the  trials  can  be  reduced  for  purposes  of 
comparison.  The  method  of  doing  this 
is  to  transform  the  evaporation,  as  deter- 
mined under  the  actual  feed  temperature 
and  steam  pressure  noted  during  the  test, 
into  an  equivalent  evaporation  based  upon 
a  standard  feed  water  temperature  of  212° 
F.,  and  a  steam  pressure  equal  to  normal 
atmospheric  pressure  at  sea  level  (14.7  Ibs. 
absolute).  Under  these  standard  conditions 
the  steam  will  be  generated  at  a  temperature 
of  212°  from  water  at  212°.  The  number 
of  pounds  of  water  which  would  be  evaporated 
under  the  standard  conditions  by  precisely 
the  same  amount  of  heat  absorbed  by  the 


6g 


O 
H 
O 


STEAM  PRESSURES,  POUNDS  BY  GAUGE.* 

0 
0 

X  ?5 

The  values  for  intermediate  pressures  and  feed  water  temperatures  may,  with  sufficient  accuracy  for  all  practical  purposes,  be  obtained  by  interpola- 
tion. If  exact  values  are  necessary  they  may  be  computed  by  the  Formula 

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When 


FACTORS   OF    EVAPORATION 


71 


Doiler  under  the  actual  test  conditions  is 
called  the  equivalent  evaporation  from  and  at 
212°;  the  quotient  of  the  equivalent  evapora- 
tion from  and  at  212°,  divided  by  the  actual 
evaporation  under  test  conditions,  is  the 
factor  of  evaporation.  For  example,  suppose 
a  boiler  to  evaporate  water  from  a  feed  tem- 
perature of  60°  F.  into  steam  at  60  Ibs. 


pound  of  water,  or  the  latent  heat  of  evapora- 
tion, would  have  been  needed,  hence  for  each 
pound  of  water  the  boiler  evaporated  under 
the  actual  conditions,  it  could  have  evaporated 

-^—  =  1. 1 88  Ibs.  of  water  from  and  at  212°. 

965.8 

Similarly,    in    another    case     it    might    be 
found  that  for  each  pound  evaporated  under 


TABLE  15 

PROPERTIES    OF    SATURATED    STEAM    FOR    VARYING 
AMOUNTS    OF    VACUUM* 


Pressure 
Above 
Vacuum. 
Lbs.  persq.in. 

Vacuum 
in 
Inches  of 
Mercury 

Temperature, 
Degrees 
Fahrenheit. 

Heat  of  the 
Liquid  above 
32°  Fahrenheit, 
B.  T.  U. 

Latent  Heat 
above 
32°  Fahrenheit, 
B.  T.  U. 

Total  Heat 
above 
32°  Fahrenheit, 
B.  T.  U. 

Density  or 
Weight  per 
Cubic  Foot, 
Pounds. 

-245 

29^ 

58.8 

26.84 

1072  .  6 

1099.5 

0.00077 

.490 

29 

79-3 

47.40 

1058.3 

1105.7 

o  .  00152 

•735 

28^ 

92  .0 

60  .  04 

1049  .6 

1109  .6 

0.00223 

.980 

28 

101.4 

69.47 

1043.1 

1112.5 

i  .00294 

i-47 

27 

ii5-3 

83.36 

1033-4 

1116.8 

o.  00431 

i  .96 

26 

125.6 

93-73 

1026  .  i 

1119.8 

0.00566 

2-45 

25 

133-9 

IO2  .  I 

1020  .  3 

1122.4 

0.00699 

2-94 

24 

140.9 

109  .  I 

1015.5 

i  124.  6 

0.00829 

3-43 

23 

147.0 

II5-3 

IOI  I  .  I 

1126.4 

0.00961 

3  92 

22 

!52-3 

I2O.6 

1007  .4 

1128  .0 

o  .01087 

4.41 

21 

J57-2 

125.6 

1003.9 

1129  .  6 

0.01218 

4.90 

20 

161.5 

129.9 

1000.9 

1130.9 

0.01342 

5-39 

19 

165.6 

134    0 

998.1 

1132.1 

0.01468 

5.88 

18 

169.4 

137.9 

995-3 

ii33-2 

0.01594 

6-37 

17 

172.8 

141.3 

992.9 

1134.2 

0.01719 

6.86 

16 

176.0 

144.5 

990.7 

II35-2 

0.01839 

7-35 

i5 

179.1 

147.6 

988.5 

1136.2 

o  .  01963 

7.84 

U 

182.  i 

150.6 

986.4 

H37-I 

0.02087 

8.82 

12 

187.5 

156.1 

982.7 

1138.7 

0.02334 

9.80 

TO 

192.4 

161  .0 

979-2 

I  140  .  2 

0.02576 

12.25 

5 

203.1 

171.8 

971.7 

IJ43-5 

0.03178 

14.  69 

0 

212  .  I 

180.9 

965.3 

1146.  2 

0.03765 

gauge  pressure.  The  total  heat  above  32° 
in  a  pound  of  steam  at  60  Ibs.  gauge  (74.7 
Ibs.  absolute)  is  1175.6  B.  T.  U.  But  since 
the  water  was  originally  at  60°  instead  of 
32°,  the  heat  added  by  the  boiler  was  only 
ii7S.6-(6o-32)  =  1147.6  B.  T.  U.  Had  this 
same  heat  been  used  to  evaporate  steam  at 
atmospheric  pressure  from  water  already  at  a 
temperature  of  212°,  only  965.8  B.  T.  U.  per 


the  actual  conditions  the  same  heat  would 
evaporate  1.121  pounds  of  water  from  and 
at  212°.  The  values  1.188  and  1.121  are 
the  factors  of  evaporation,  or  the  factor  by 
which  the  number  of  pounds  of  water  in  the 
actual  test  is  to  be  multiplied  to  find  the 
equivalent  number  of  pounds  that  could  be 
evaporated  from  and  at  212°  F.  with  the  same 
amount  of  heat.  This  factor  for  any  set  of 


*Partly  from  S.  A.  Reeve,  The  Thermodynamics  o'f  Heat  Engines,  1903. 


72  THE    STIRLING    WATER 

conditions  may  be  determined  by  the  formula : 


965.8 

in  which  H=total  heat  of  steam  above  32° 
from  steam  table;  *=temperature  Fah.  of  feed 
water. 

Table   16  gives  the  factors  of   evaporation 
for  a  large  range  of  conditions,  and  for   all 


-TUBE    SAFETY    BOILER 

changes  according  to  altitude  and  the  varia- 
tions of  the  barometer.  Consequently  cal- 
culations involving  the  properties  of  steam 
are  based  on  absolute  pressure,  which  is 
equal  to  the  gauge  pressure  plus  the  atmos- 
pheric pressure  in  pounds  per  square  inch. 
The  latter  is  usually  assumed  to  be  equal 
to  14.7  pounds  per  sq.  inch  at  sea  level,* 


TABLE  17 

RATE    OF    VARIATION    OF    PROPERTIES    OF    SATURATED    STEAM 
AT    VARIOUS    PRESSURES 


Abso- 
lute 
Pres- 
sure. 
Lbs.  per 
sq.  in. 

Temper- 
ature. 
Deg.  Fahr. 

Increase  in 
Temperature 
per  Pound 
of  Pressure. 
Deg.  Fahr. 

Heat  of  the 
Liquid. 
B.  T.  U. 

Increase  in 
Heat  of  the 
Liquid,  per 
Pound  of 
Pressure. 
B.  T.  U 

Latent 
Heat. 
B.  T.  U. 

Decrease  in 
Latent  Heat 
per  Pound 
of  Pressure. 
B.  T.  U. 

Total  Heat. 
B.  T.  U. 

Increase  in 
Total  Heat 
per  Pound 
of  Pressure. 
B.  T.  U. 

Per  Cent,  of 
Total  Heat 
as  Heat  of 
Liquid. 

20 

227.9 

196.9 

954-6 

"S^S 

17-3 

I  .96 

1.98 

I.38 

•595 

40 

267  .  I 

236.4 

927.0 

1163.4 

20.3 

1.27 

1.28 

.885 

•  390 

60 

292.5 

26l  .9 

9°9-3 

1171.2 

22  .  4 

-965 

•975 

.685 

.  290 

80 

3II.8 

281.4 

895.6 

1177.0 

23-9 

.830 

.825 

.580 

•  245 

IOO 

327.6 

297.9 

884. 

1181  .  9 

25.2 

.614 

.642 

•456 

.186 

ISO 

358-3 

330-0 

861  .2 

1191.2 

27.7 

.468 

.492 

.348 

.144 

2OO 

38I-7 

354-6 

843.8 

1198.4 

29.8 

•357 

•373 

.  264 

.  109 

•300 

417.4 

391-9 

817.4 

1209.3 

32-4 

•275 

.279 

•195 

.084 

4OO 

444-9 

419.8 

797-9 

1217.7 

34-5 

•  225 

•237 

.  169 

.068 

500 

467.4 

443-5 

781  .0 

1224.5 

35-5 

.179 

.  190 

•135 

•  054 

750 

512.1 

490.9 

747-2 

1238.0 

39-6 

•139 

.149 

.107 

-043 

1000 

546.8 

528.3 

720.3 

1248.7 

42.4 

except  the  most  refined  work  the  omitted 
values  may  be  determined  by  interpolation. 

A  Unit  of  Evaporation  is  the  quantity 
of  heat  necessary  to  evaporate  one  pound 
of  water  at  212°  into  steam  at  the  same 
temperature,  and  is  equal  to  965.8  B.  T.  U. 
Its  symbol  is  U.  E. 

Absolute  and  Gauge  Pressures — Steam 
gauges  indicate  the  pressure  above  the  at- 
mosphere. The  atmospheric  pressure 

*See  Table  12,  page  58. 


but  for  other  levels  it  must  be  determined 
from  the  barometer  reading  at  that  place. 
Vacuum  gauges  indicate  the  difference, 
expressed  in  inches  of  mercury,  between 
atmospheric  pressure  and  the  pressure  inside 
the  vessel  to  which  the  gauge  is  attached. 
For  all  rough  purposes  two  inches  height 
of  mercury  may  be  considered  equal  to 
pressure  of  one  pound  per  square  inch,  hence 
for  any  reading  of  the  vacuum  gauge  the 


STEAM   TABLES 


73 


absolute  pressure  will  be  14.7 -^X  gauge 
reading  in  inches.  Example:  vacuum  of 
24  inches  will  equal  14.7-12=2.7  Ibs. 
absolute  per  sq.  inch. 

Table  15  gives  the  temperature,  pressure 
and  other  properties  of  steam  for  varying 
amounts  of  vacuum,  and  exact  pressures 
corresponding  to  each  inch  of  reading  of 
vacuum  gauge. 

Economy  of  High  Pressure  Steam — 
From  the  steam  tables  the  following  con- 
densed table  of  the  heat  needed  at  different 
pressures  may  be  constructed. 


ABSOLUTE 
PRESSURE. 

TEMPER- 
ATURE F. 

HEAT    OF 
LIQUID. 

LATENT 
HEAT. 

TOTAL 
HEAT. 

T4-7 

212 

I80.8 

965.8 

II46.6 

20.  o 

228 

196.9 

954-6 

IJ5i-5 

IOO.O 

327.6 

297.9 

884.0 

1  181  .  9 

301.9 

4l8 

392.5 

816.9 

1209.4 

From  this  the  following  conclusions  can 
be  drawn. 

As  the  pressure  and  temperature  increase, 
the  latent  heat  decreases,  but  less  rapidly 
than  heat  of  the  liquid  increases,  hence  the 
total  heat  increases.  The  percentage  in- 
crease of  total  heat  is  very  small,  being  for 
the  pressures  of  20,  100  and  301.9  pounds 
absolute,  only  0.43,  3.0  and  5.4  per  cent, 
respectively,  more  than  required  for  the 
pressure  of  14.7  Ibs.  The  temperatures, 
however,  increase  at  the  rates  of  7.5,  54.5 
and  97.1  per  cent.  The  efficiency  for  a 
perfect  steam  engine  is  proportional  to  the 

t—t. 
expression — —Sin  which  t  and/j  are  absolute 


temperatures  of  steam  at  admission  and 
exhaust,  respectively.  In  actual  engines 
the  efficiency  only  approximates  to  the 
ideal,  yet  it  will  follow  the  same  general 
law.  Since  the  exhaust  temperature  cannot 
be  lowered  beyond  present  practise  it  follows 
that  the  only  available  method  of  increasing 
the  efficiency  is  to  raise  the  temperature 
at  admission,  which  means  either  higher 
steam  pressure,  or  use  of  superheated  steam. 
As  above  shown,  the  increase  in  pressure 
will  require  but  a  trifling  increase  in  fuel, 
hence  the  higher  the  pressure  the  greater 
the  economy. 

Steam  Tables — Up  to  the  present  time 
an  algebraic  expression  for  the  relation 
between  saturated  steam  pressures,  tem- 
peratures, and  volumes,  has  not  been  pro- 
duced, except  empirically.  These  relations 
have,  however,  been  experimentally  de- 
determined  by  Regnault,  and  from  his  data 
steam  tables  have  been  computed.  These 
obviate  the  necessity  of  using  empirical 
formulas.  Such  formulas  may  be  found  in 
standard  works  on  Thermodynamics,  and 
a  number  of  them  are  given  in  Peabody's 
work  below  referred  to.  The  following  named 
tables  cover  all  practical  cases: 

Table  15  gives  properties  of  saturated 
steam  for  varying  amounts  of  vacuum. 

Table  17  shows  variation  in  properties 
of  steam  at  different  pressures. 

Table  18  gives  properties  of  saturated 
steam  from  2  to  500  pounds  absolute.  These 
tables  are  based  partly  on  Prof.  Cecil  H. 
Peabody's  Tables  of  the  Properties  of  Satu- 
rated Steam,  which  are  generally  accepted  by 
engineers. 


74 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


TABLE    18 
PROPERTIES   OF   SATURATED   STEAM 


*  Pressure  above 
Vacuum. 
Lbs.  per  sq.  in. 

Temperature, 
Degrees 
Fahrenheit. 

Heat  of  Liquid 
above  32°Fahr. 
B.  T.  U. 

Latent  Heat 
above  32°  Fahr. 
B.  T.  U. 

Total  Heat 
above  32°  Fahr. 
B.  T.  U. 

Density,  or  Weight 
per  Cubic  Foot. 
Pounds. 

2 

126.3 

94-4 

1026.  i 

1120.5 

0.00576 

4 

I53-I        . 

121.4 

IOO7  .  2 

1128.6 

0.01107 

6 

170  .  i 

138.6 

995-2 

H33-8 

o  .  01622 

8 

182.9 

I5I-5 

986.2 

H37-7 

0.02125 

10 

193-3 

161  .9 

979-o 

1140.9 

o  .  02621 

12 

202  .  o 

170.7 

972-9 

1143.6 

o  .  031  i  i 

14 

209  .6 

178.3 

967-5 

1145.8 

o  .  03600 

14-7 

212  .  O 

180.8 

965.8 

1146.6 

0.03760 

16 

216.3 

185.1 

962.8 

1147.9 

o  .  04067 

18 

222  .4 

i9i-3 

958.5 

1149  .8 

0.04547 

20 

228.0 

196.9 

954-6 

"Si-5 

o  .  05023 

22 

233-1 

202  .O 

951-0 

iJ53-o 

0.05495 

24 

237-8 

206.8 

947-6 

ii54-4 

0.05966 

26 

242  .  2 

211  .  2 

944-6 

H55-8 

o  .06432 

28 

246.4 

215-4 

941.7 

ii57-i 

0.06899 

3° 

25°-3 

219.4 

938.9 

1158.3 

0.07360 

32 

254.0 

223.1 

936.3 

1159-4 

0.07821 

34 

257-5 

226.  7 

933-7 

i  i  60  .  4 

o  .08280 

36 

260.  9 

230.0 

93J-5 

1161.5 

0.08736 

38 

264.  i 

233-3 

929.  2 

1162.5 

o  .  09191 

40 

267  .  i 

236.4 

927  .0 

1163.4 

o  .  09644 

42 

270.  i 

239-3 

925.0 

1164.3 

o.  1009 

44 

272.9 

242  .  2 

923.0 

1165.2 

0.1054 

46 

275-7 

245.0 

921  .O 

1166.0 

o  .  1099 

48 

278-3 

247.6 

919.2 

1166.8 

o.  1144 

5° 

280.9 

250.2 

917.4 

1167  .6 

0.1188 

52 

283-3 

252.7 

9*5-7 

1168.4 

0.1233 

54 

285.7 

255-1 

914.0 

1169  .  i 

o.  1277 

56 

288.1 

257-5 

912.3 

1169.8 

0.1321 

58 

290.3 

259-7 

910.8 

1170.5 

o  .  1366 

60 

292.5 

26l  .9 

909-3 

1171.2 

o.  1409 

62 

294.7 

264.  I 

907.7 

1171.8 

0.1453 

64 

296.7 

266  .  2 

906.  2 

1172.4 

o.  1497 

66 

298.8 

268.3 

904.7 

1173.0 

0.1541 

68 

300.8 

270.3 

903-3 

1173.6 

0.1584 

70 

302.7 

272.2 

902  .  I 

H74.3 

0.1628 

72 

304.6 

274.1 

9O0.8 

1174.9 

o.  1671 

74 

306.5 

276.0 

899.4 

II75-4 

0.1714 

76 

308.3 

277-8 

898.2 

1176  .0 

0.1757 

78 

310.1 

279.6 

896.9 

1176.5 

o.  1801 

80 

311.8 

28l  .4 

895.6 

1177.0 

0.1843 

82 

3I3-S 

283.2 

894  4 

1177.6 

0.1886 

84 

315-2 

285.0 

893-1 

1178.1 

0.1930 

86 

316.8 

286.7 

891.9 

1178.6 

o.i973 

88 

318.5 

288.4 

890.7 

1179.1 

o.  2016 

*To  reduce  to 
above  sea  level, 


gauge  pressures  at 
subtract  pressures 


sea  level,  subtract 
per  square  inch  as 


14.7  from 
in  Table  1 2 


pressures  in  this  column. 
,  page  58. 


In  altitudes 


STEAM    TABLES 
PROPERTIES    OF    SATURATED    STEAM.— CONTINUED 


75 


*  Pressure  above 
Vacuum. 
Lbs.  Per  sq.  in. 

Temperature, 
Degrees 
Fahrenheit. 

Heat  of  Liquid 
above  32  J  Fahr. 
B.  T.  U. 

Latent  Heat 
above  32°  Fahr. 
B.  T.  U. 

Total  Heat 
above  32°  Fahr. 
B.  T.  U. 

Density,  or  Weight 
Per  Cubic  Foot. 
Pounds. 

90 

320.0 

290  .  o 

889.6 

1179.6 

o.  2058 

92 

321  .6 

291  .6 

888.4 

1180.0 

0.  2101 

94 

323-i 

293.2 

887.3 

1180.5 

o  .  2144 

96 

324.6 

294.8 

886.2 

1  181  .0 

0.2186 

98 

326.1 

296  .  4 

885.0 

1181  .4 

o  .  2229 

IOO 

327.6 

297-9 

884.0 

1  181  .9 

o.  2271 

102 

329.0 

299.4 

882.9 

1182.3 

0.2314 

IO4 

330-4 

300.9 

881.8 

1182.7 

0.2356 

106 

331-8 

3°2-3 

880.8 

1183.1 

0.2399 

108 

333-2 

303-8 

879.8 

1183.6 

o  .  2441 

no 

334-6 

305-2 

878.8 

i  184  .  o 

o.  2484 

112 

335-9 

306.6 

877.8 

1184.4 

o  .  2526 

114 

337-2 

308.0 

876.8 

1184.8 

0.2568 

116 

338.5 

3°9-4 

875.8 

1185.2 

o.  2610 

118 

339-8 

310.7 

874.9 

1185.6 

0.2653 

120 

34i-i 

312.0 

874.0 

1186.0 

0.2695 

122 

342.3 

3I3-3 

873-o 

1186.3 

0.2736 

I24 

343-5 

3J4-6 

872.  i 

1186.7 

0.2779 

126 

344-7 

3I5-9 

871  .2 

1187.1 

o  .  2820 

128 

345-9 

3J7-1 

870.3 

1187.4 

o.  2862 

130 

347  -1 

318.4 

869.4 

1187.8 

o.  2904 

132 

348.3 

319.6 

868.6 

1188.2 

o  .  2946 

134 

349-5 

320.8 

867.7 

1188.5 

0.2988 

I36 

35°-6 

322.0 

866.9 

1188.9 

0.3030 

138 

35x-7 

323  •  2 

866.0 

1189  .  2 

0.3072 

I4O 

352-9 

324-4 

865.1 

1189.5 

0-3ri3 

142 

354-o 

325-6 

864.3 

i  189  .  9 

0.3155 

144 

355-1 

326.7 

863.5 

1190.  2 

o.3i97 

146 

356-1 

327-8 

862.8 

i  190  .  6 

0.3239 

148 

357-2 

328.9 

862.0 

1190.9 

o.  3280 

150 

358.3 

330.0 

861.2 

1191.2 

0.3321 

152 

359-3 

331-1 

860.4 

1191.5 

0.3363 

J54 

360.3 

332-2 

859.6 

1191  .  8 

0.3405 

156 

361.4 

333-3 

858.9 

1192  .  2 

0.3447 

158 

362.4 

334-3 

858.2 

1192.5 

0.3488 

1  60 

363-4 

335-4 

857-4 

1192  .8 

0.3530 

162 

364-4 

336.4 

856.7 

1193.1 

0-3572 

164 

365-4 

337-5 

855-9 

II93-4 

0.3614 

166 

366.4 

338.5 

855-2 

II93-7 

0.3655 

168 

367-3 

339-5 

854.5 

1194.0 

o  3695 

170 

368.3 

340.5 

853-8 

ii94-3 

0.3737 

172 

369-2 

34i-5 

853-I 

i  194  .  6 

0.3778 

174 

370.2 

342.5 

852-3 

1194.8 

o.  3820 

176 

371-1 

343-5 

851.6 

1195.1 

o.  3862 

178 

372-1 

344-4 

851.0 

II95-4 

0.3904 

180 

373-o 

345-4 

850-3 

JI95-7 

0-3945 

*To  redtice  to  gauge  pressures  at  sea  level,  subtract  14.7  from  pressures  in  this  column.      In  altitudes 
above  sea  level,  subtract  pressures  per  square  inch  as  in  Table  12,  page  58. 


76 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 
PROPERTIES  OF  SATURATED  STEAM.— CONTINUED 


*  Pressure  above 
Vacuum. 
Lbs.  per  sq.  in. 

Temperature, 
Degrees 
Fahrenheit. 

Heat  of  Liquid 
above  32°Fahr. 
B.  T.  U. 

Latent  Heat 
above  32°  Fahr. 
B.  T.  U. 

Total  Heat 
above  32°  Fahr. 
B.  T.  U. 

Density,  or  Weight 
per  Cubic  Foot. 
Pounds. 

182 

373-9 

346.4 

849.6 

1196.0 

0.3987 

184 

374-8 

347-3 

848.9 

I  196  .  2 

o.  4029 

186 

375-7 

348.2 

848.3 

1196.5 

o.  4070 

1  88 

376.6 

349   2 

847.6 

1196.8 

0.4111 

190 

377-4 

350-1 

847.0 

II97.I 

0.4153 

192 

378.3 

351   o 

846.3 

"97-3 

0.4194 

194 

379-2 

35J-9 

845.7 

1197.6 

0.4236 

196 

380.0 

352.8 

845.0 

1197.8 

0.4278 

198 

380.9 

353-7 

844.4 

1198.  i 

0.4318 

200 

381-7 

354-6 

843-8 

1198.4 

0-4359 

2O2 

382.6 

355-4 

843-2 

1198.6 

0-4399 

2O4 

383-4 

356.3 

842.6 

1198.9 

0.4441 

206 

384-2 

357-2 

841.9 

1199.1 

o.  4482 

208 

385-1 

358.o 

841.4 

1199.4 

0.4524 

2IO 

385-9 

358.9 

840.7 

1199  .  6 

0.4565 

212 

386.7 

359-7 

840.  2 

1199.9 

0.4607 

214 

387.5 

360  .  6 

839.5 

i  200.  i 

0.4648 

2x6 

388.3 

361-4 

839.0 

1200.4 

o  .  4690 

218 

389.1 

362.2 

838.4 

i  200  .  6 

o  4731 

22O 

389.8 

363-0 

837.8 

1200.8 

0.4772 

222 

390.6 

363-9 

837-2 

I2OI  .  I 

0.4813 

224 

39x-4 

364.7 

836.6 

1201.3 

0.4855 

226 

392.2 

365-5 

836.1 

I2OI  .  6 

0.4896 

228 

392.9 

366.3 

835  5 

I2OI  .  8 

0.4939 

230 

393.7 

367   i 

834-9 

1202  .O 

0.4979 

232 

394-5 

367   9 

834-3 

I2O2  .  2 

o.  5021 

234 

395-2 

368.6 

833-9 

I2O2  .  5 

o.  5062 

236 

395-9 

369-4 

833-3 

I2O2  .  7 

0.5103 

238 

396.7 

370.2 

832-7 

I2O2  .9 

0.5144 

24O 

397-4 

371-0 

832.2 

I2O3  .  2 

0.5186 

242 

398.1 

37T-7 

831-7 

1203.4 

o.  5226 

244 

398.9 

372-5 

831.1 

1203  .6 

0.5268 

246 

399-6 

373-2 

830.6 

1203.8 

0-5311 

248 

400.3 

374-0 

830.0 

1204.0 

0-5353 

250 

401  .  o 

374-7 

829.5 

I2O4.  2 

0-5393 

252 

401  .7 

375-4 

829.1 

1204.5 

0-5433 

254 

402.4 

376.2 

828.5 

1204-7 

0-5475 

256 

403-1 

376.9 

828.0 

1204.9 

o  55J7 

258 

403.8 

377-6 

827-5 

I205.I 

0-5559 

260 

404-5 

378.4 

826.9 

1205.3 

o.  5601 

262 

405.2 

379-1 

826.4 

!205.5 

0.5642 

264 

405.8 

379-8 

825.9 

1205.7 

0.5684 

266 

406.5 

380.5 

825.4 

1205.9 

0.5726 

268 

407.2 

381-2 

824.9 

1206  .  I 

0.5767 

270 

407-9 

381.9 

824.4 

1206.3 

0.5809 

?72 

408.5 

382.6 

823.9 

1206.  5 

0.5850 

*To  reduce  to  gauge  pressures  at  sea  level,  subtract  14.7  from  pressures  in  this  column, 
above  sea  level,  subtract  pressures  per  square  inch  as  in  Table  12,  page  58. 


In  altitudes 


STEAM    TABLES 
PROPERTIES  OF  SATURATED  STEAM.— CONTINUED 


77 


*Pressure  above 
Vacuum. 
Lbs.  per.  sq.  in. 

Temperature, 
Degrees 
Fahrenheit. 

Heat  of  Liquid 
above  32°  Fahr 
B.T.  U. 

Latent  Heat 
above  32°  Fahr. 
B.T.  U. 

Total  Heat 
above  32°  Fahr. 
B.  T.  U. 

Density,  or  Weight 
per  Cubic  Foot. 
Pounds  . 

274 

409.2 

383.3 

823.4 

1206.  7 

0.5892 

276 

409  .8 

384.0 

822  .9 

1206  .  9 

0-5934 

278 

410.5 

384.6 

822.5 

1207  .  i 

0.5976 

280 

411.1 

385.3 

822  .0 

1207.3 

o.  602 

282 

411.8 

386.0 

821.5 

1207.5 

o  .  606 

284 

412.4 

386.6 

821.1 

1207.7 

o.  610 

286 

413-° 

387-3 

820.6 

1207  .  9 

0.614 

288 

4I3-7 

388.0 

820.1 

1208.  i 

0.618 

290 

4I4-3 

388.6 

819.7 

1208.  3 

o  .  622 

292 

414.9 

389-3 

819.2 

1208.5 

0.627 

294 

4i5-6 

390.0 

818.7 

1208  .  7 

0.631 

296 

416.  2 

390.6 

818.3 

1208  .  9 

0-635 

298 

416.8 

391-3 

817.8 

1209  .  i 

0.639 

300 

4I7-4 

391-9 

817.4 

1209.3 

0.644 

302 

4l8.O 

392-5 

816.9 

1209  .  4 

0.648 

3°4 

418.6 

393-2 

816.4 

1209  .  6 

0.652 

306 

419.2 

393-8 

816.0 

1209  .8 

0-656 

308 

419.8 

394-4 

815.6 

I2IO  .  O 

0.660 

310 

420.4 

395-° 

815.2 

I2IO.  2 

o.  664 

312 

421  .  o 

395-7 

814.7 

1210.4 

0.668 

3U 

421  .6 

396.3 

814.2 

1210.5 

0.673 

3i6 

422  .  2 

396.9 

813.8 

1210.7 

0.677 

3i8 

422.8 

397-5 

8i3-4 

1210.9 

0.681 

320 

423-4 

398.1 

813.0 

I2II  .  I 

0.685 

322 

424.0 

398.7 

812.5 

121  I  .  2 

0.690 

324 

424-5 

399-3 

812.  i 

I2II.4 

0.694 

326 

425.1 

399-9 

811.7 

121  I  .  6 

0.698 

328 

425-7 

400.5 

811.3 

I2II.8 

o.  702 

33° 

426.  2 

401  .  i 

810.8 

I2II.9 

0.707 

335 

427.6 

402  .6 

809.8 

1212  .4 

0.717 

35° 

43J-9 

406.9 

806.8 

1213.7 

0.748 

375 

438-4 

414.2 

801.5 

1215.7 

0.800 

400 

445-2 

421.4 

796.3 

1217.7 

0-853 

45° 

456.2 

433-4 

787.7 

1221  .  I 

°-959 

500 

466.6 

444-3 

779-9 

1224.  2 

1.065 

*To  reduce  to  gauge  pressures  at 

above  sea  level,  subtract  pressures 

For  relation  between  Heat  of  the 


sea  level,  subtract  14.7  from  pressures  in  this  column. 

per  square  inch  as  in  Table  12,  page  58. 

Liquid,  Latent  Heat,  and  Total  Heat,  see  page  50. 


In  altitudes 


Moisture  in  Steam 


Practically  all  saturated  steam  contains 
water,  varying  in  amount  from  a  fraction  oi 
one  per  cent,  when  the  steam  is  generated  in 
a  properly  designed  boiler  fed  with  good 
water,  to  five  per  cent,  or  even  more  when 
the  feed  water  is  bad,  or  the  boilers  are  of 
defective  design.  Not  only  is  the  heat 
absorbed  by  raising  this  water  from  the 
boiler  feed  temperature  to  the  steam  tem- 
perature practically  wasted,  but  the  water 
causes  further  loss  by  increasing  the  initial 
condensation  in  the  engine  cylinder;  it  also 
interferes  with  proper  cylinder  lubrication, 
causes  knocking  in  the  engine,  and  water 
hammer  in  the  steam  pipe. 

Quality  of  Steam — The  percentage  weight 
of  steam,  in  a  mixture  of  steam  and  water,  is 
called  the  quality  of  the  steam.  Thus  steam 
of  quality  99.5  contains  one-half  of  one  per 
cent,  by  weight  of  moisture. 

Calorimeters — The  apparatus  used  to  de- 
termine the  content  of  moisture  in  steam  is 
called  a  calorimeter,  though  the  name  is  inapt, 
since  the  instrument  is  in  no  sense  a  measurer 
of  heat.  The  first  form  used  was  the  "barrel 
calorimeter,''  in  this  apparatus  liability  of 
error  is  so  great  that  its  use  is  practically 
abandoned.  Modern  calorimeters  are  usually 
of  either  the  throttling  or  separator  type. 

Throttling  Calorimeter — Fig.  14  shows  a 
section  through  a  typical  form  of  the  instru- 
ment. Steam  is  drawn  from  the  vertical 
pipe  by  a  nipple  arranged  as  later  described, 
passes  around  the  first  thermometer  cup  as 
shown,  then  through  a  hole  about  ^-inch 
diameter  in  the  disk  as  shown.  It  next 
passes  around  the  lower  thermometer  cup, 
after  which  it  is  permitted  to  escape.  Ther- 
mometers are  inserted  into  the  cups,  which  are 
then  filled  with  cylinder  oil,  and  when  the 
whole  apparatus  is  heated  the  temperature 
of  the  steam  before  and  after  passing  through 
the  hole  in  the  disk  is  noted. 

The  instrument  and  pipes  leading  to  it 
should  be  thoroughly  covered  to  diminish 
the  radiation  loss. 

When  steam  passes  from  a  higher  to  a 
lower  pressure,  as  in  this  case,  no  work  has  to 
be  done  in  overcoming  a  resistance;  hence, 


assuming  there  is  no  loss  from  radiation,  the 
quantity  of  heat  is  exactly  the  same  after 
passing  the  disk  as  it  was  ahead  of  it.  Sup- 
pose that  the  higher  steam  pressure  is  150 
Ibs.  by  gauge,  and  the  lower  pressure  that  of 
the  atmosphere.  The  total  heat  in  a  pound 
of  dry  steam  at  the  former  pressure  is  1193.5 
B.  T.  U.  and  at  the  latter  pressure  is  1146.6 
B.  T.  U.,  difference,  46.9  B.  T.  U.  As  this 
heat  still  exists  in  the  steam  of  lower  pressure, 


TO  ATMOSPHERE  - 

FIG.  14.     THROTTLING  CALORIMETER  AND  SAMPLING  PIPE 

its  effect  is  to  superheat  that  steam.  Assum- 
ing the  specific  heat  of  steam  to  be  0.48,  the 

46.9 

steam  will  then  be  superheated    -  —^  =  97.7 

0.40 

degrees.  Suppose,  however,  the  steam  had 
contained  one  per  cent,  of  moisture.  Before  any 
superheating  could  occur,  this  moisture  would 
have  to  be  evaporated  into  steam  of  atmos- 
pheric pressure .  Since  the  latent  heat  of  steam 
at  atmospheric  pressure  is965.8B.T.U.it  fol- 
lows that  the  one  per  cent,  of  moisture  would 
require  9.58  B.  T.  U.  to  evaporate  it,  leaving 
only  46.9  -  69.658  =  37.242  B.  T.  U.  available 
for  superheating,  hence  the  superheat  would 

37.242 
be —  =>  77.6°   as  against  97.7  degrees  in 

the  preceding  case.  In  a  similar  manner  the 
degree  of  superheat  for  other  amounts  of 
moisture  can  be  determined,  and  the  action 
of  the  throttling  calorimeter  is  based  on  this 
fact  as  will  now  be  shown. 


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FORMULAS    FOR    THROTTLING    CALORIMETER 


81 


Let  H=  total  heat  of  steam  at  boiler  press- 
ure. 

L  =  latent  heat  of  steam  at  boiler  press- 
ure. 

h  =  total  heat  of  steam  at  reduced  press- 
ure after  passing  the  disk. 
*j  =  temperature  of   saturated  steam  at 

the  reduced  pressure. 
ta  =  temperature  of  steam  after  expand- 
ing through  opening  in  the  disk. 
0.48=  specific  heat  of  saturated  steam. 

x  =  proportion  of  moisture  in  the  steam. 
The  difference  between  the  B.  T.  U.'s  in  a 
pound  of  steam  at  boiler  pressure  and  after 
passing  the  disk  is  the  heat  which  must 
evaporate  the  moisture  in  the  steam,  and 
then  do  the  superheating,  hence 

H—h=xL—o.4S(t2—t1),    therefore 


H-h-o.. 


-  *,) 


[6] 

i^, 

Almost  invariably  the  lower  pressure  is  ta- 
ken as  that  of  the  atmosphere  where 
/t==ii46.6  and  ^=212,  hence  the  formula  be- 
comes 

H— 1146.6  —  0.48  (tz—  212) 

For  practical  work  it  is  more  convenient  to 
dispense  with  the  upper  thermometer  in  the 
calorimeter,  and  substitute  an  accurate  steam 
guage  whose  readings  are  more  easily  noted. 

The  value  of  x  may  be  obtained,  without 
computation,  from  Fig.  15.  To  illustrate 
its  use,  suppose  that  the  steam  gauge  on  the 
calorimeter  indicated  160  pounds  pressure, 
and  that  the  temperature  tz  in  the  calorimeter 
after  the  steam  had  expanded  was  304°. 
Look  on  the  bottom  line  of  the  chart  and 
locate  the  vertical  line  over  304°;  look  into 
the  gauge  pressure  scale  on  the  left  side  of  the 
chart,  and  locate  the  horizontal  line  opposite 
1 60  pounds;  these  two  lines  intersect  the- 
diagonal  line  indicating  one-half  of  one  per 
cent,  of  moisture.  If  instead  of  a  steam  gauge 
to  indicate  the  pressure,  a  thermometer  had 
been  used  to  indicate  the  temperature  of  the 
steam  before  expanding,  the  temperature  on 
the  upper  thermometer  would  have  been  370°, 
and  the  column  of  temperatures  on  the  ex- 
treme left  hand  of  the  chart  would  be  the  one 
to  use;  the  horizontal  line  opposite  370°  will 
be  found  to  be  the  same  one  which  is  opposite 


1 60   pounds   pressure,    hence    as   before   the 
moisture  will  be  one-half  of  one  per  cent. 

Sources  of  Error — There  are  two.  The 
first  is  that  the  specific  heat  of  superheated 
steam,  while  given  as  0.48,  is  far  from  being 
certain,  and  only  future  investigation  can 
determine  the  true  value.  The  second  source 
of  error  is  loss  of  heat  by  radiation.  Evi- 
dently from  the  moment  the  steam  enters 
the  sampling  nipple  it  is  losing  heat,  hence 
when  it  passes  through  the  small  opening  and 
into  the  lower  pressure  the  heat  available  for 
evaporating  moisture  and  superheating  will 
be  diminished  by  just  the  amount  lost  by 
radiation,  hence  the  value  of  tz  will  be  lower 
than  it  should  be.  This  is  sometimes  cor- 
rected for  as  follows:  A  valve  in  the  steam 
pipe  beyond  the  calorimeter  nipple  is  closed, 
and  the  steam  left  in  a  quiescent  state  for 
about  ten  minutes,  and  it  is  assumed  that  by 
doing  this  all  the  moisture  in  the  steam  will 
settle  out,  and  that  a  sample  of  steam  drawn 
from  the  pipe  will  be  dry.  Steam  is  then 
allowed  to  flow  through  the  calorimeter  and 
the  temperature  of  the  lower  thermometer  is 
noted.  Let  T  denote  this  temperature. 
Since  the  sample  of  steam  was  assumed  to  be 
dry  it  follows  that  if  there  were  no  loss  from 
radiation  the  value  of  T  would  be  that  due 
to  all  of  the  liberated  heat  being  absorbed 
in  superheating  the  steam  of  lower  tempera- 
ture. There  is,  however,  a  loss  by  radiation, 
and  the  effect  of  this  is  to  condense  some  of 
the  steam  of  lower  pressure,  and  the  water 
thus  formed  must  be  evaporated  before  any 
superheating  can  be  done.  Let  x1  represent 
the  proportion  of  water  thus  formed, then 
evidently 


L 

Now  this  amount  of  water  was  not  in  the 
steam  originally,  but  was  caused  by  con- 
densation in  the  instrument,  hence  the  true 
amount  of  moisture  in  the  steam,  which  may 
be  denoted  by  X,  will  be 

H— h— 0.48  (t%— ^) 
X=x-x  -          —j— 

H-h-o.48  (T-M 


L 

0.48  (T-t9\ 
L 


[8] 


JACOB   RUPPERT   ICE   CO.,  NEW  YORK,  OPERATING   2, TOO    H.  P.  OF  STIRLING    BOILERS 


SEPARATING   CALORIMETER 


83 


The  disadvantages  of  this  method  are: 
(i)  It  assumes  that  during  the  test  the 
boiler  pressure  will  remain  the  same  as  it  was 
when  T  was  determined,  which  is  seldom 
practicable;  (2)  It  assumes  that  the  sample 
of  steam  drawn  into  the  instrument  when 
determining  T  was  absolutely  dry,  although 
experiment  has  shown  that  this  assumption 
is  not  necessarily  true.  Notwithstanding 
these  facts,  formula  [8]  is  much  used  by 
engineers  because  of  its  simplicity  and  con- 
venience, and  any  error  due  to  its  use  is  of  no 
practical  significance. 

There  are  many  forms  of  throttling  calori- 
meter, all  of  which  operate  on  precisely  the 
same  principle  as  the  simple  design  shown  in 
Fig.  14.  An  extremely  convenient  and  com- 
pact design  is  shown  in  Fig.  16.  It  consists 
of  two  concentric  cylinders  screwed  to  a  cap 
containing  a  thermometer  cup.  The  steam 
pressure  is  measured  by  a  gauge  placed  in  the 
supply  pipe,  or  any  other  convenient  place. 


FIG.  16.     COMPACT  THROTTLING  CALORIMETER 

Steam  passes  through  the  opening  A ,  expands 
to  atmospheric  pressure,  and  its  temperature 
at  this  pressure  is  measured  by  a  thermometer 
placed  in  the  cup  C.  To  prevent  radiation 
losses  the  annular  space  between  the  two 
cylinders  is  used  as  a  jacket,  and  is  supplied 
with  steam  through  the  hole  B. 


The  limits  of  the  throttling  calorimeter 
at  sea  level  are  from  about  four  per  cent,  of 
moisture  at  eighty  pounds  pressure  to  six  per 
cent,  at  200  pounds  pressure.  If  there  is  a 
greater  content  of  moisture  the  liberated  heat 
is  insufficient  to  evaporate  it  and  superheat 
the  steam  thus  generated. 


FIG.  17.     SEPARATING  CALORIMETER 

Separating  Calorimeter — The  separating 
calorimeter  mechanically  separates  the  en- 
trained water  from  the  steam  and  collects  it 
in  a  reservoir,  where  its  amount  is  either 
indicated  by  a  gauge  glass  or  determined  by 
draining  it  off  and  weighing  it.  The  steam 
passes  out  of  the  calorimeter  through  an 
orifice  of  known  size,  so  that  either  its  total 
amount  can  be  calculated  or  it  can  be  weighed 
as  later  described.  To  avoid  radiation  errors 
the  calorimeter  should  be  well  covered  with 
non-conducting  material.  This  instrument 
is  not  limited  in  capacity  theoretically,  but 
if  the  amount  of  moisture  is  very  large,  the 
readings  should  be  checked  by  passing  the 
discharged  steam  through  a  throttling  calori- 


TAKING    A    CALORIMETER    OBSERVATION 


85 


meter;  that  is,  a  small  separator  should  be 
used  between  the  steam  pipe  and  a  throttling 
calorimeter,  and  the  sum  of  the  percentages 
obtained  from  the  two  instruments  be  taken 
as  the  moisture  in  the  steam. 

In  the  separating  calorimeter,  the  amount 
of  steam  passing  through  the  orifice  can  be 
determined  by  Napier's  empirical  formula, 
page  91.  There  is  liability  of  considsrable 
erron  in  determining  the  area  of  such  small 
orifices,  and  further,  the  flow  of  steam  soon 
wears  the  orifice  larger.  A  more  accurate 
method  of  determining  the  weight  of  steam 
passing  through  is  to  convey  it  through  a  hose 
into  a  barrel  of  water  resting  on  a  platform 
scale.  The  weight  of  the  barrel  and  contained 
water  having  been  noted  before  and  after  the 
steam  is  run  in,  the  difference  is  the  weight 
of  steam  condensed.  The  moisture  caught 
in  the  separating  calorimeter  can  be  weighed 
in  the  same  way.  If  W  is  the  weight  of  steam 
condensed,  w  the  weight  of  moisture  from  the 
separating  calorimeter,  and  x  the  per  cent. 
of  moisture  in  the  steam,  then 

IOOW 

'-wTw  l9] 

Location  of  Sampling  Nipple — The  prin- 
cipal source  of  inaccuracy  in  calorimeter 
determinations  is  failure  to  secure  an  average 
sample  of  steam.  It  is  extremely  doubtful 
whether  such  a  sample  is  ever  secured.  To 
diminish  the  liability  of  error  the  instrument 
should  be  located  as  near  as  possible  to  the 
point  where  the  sample  is  drawn  off,  and  the 
sampling  nipple  should  be  placed  as  fully 
described  in  "Rules  for  Conducting  Boiler 
Trials,''  Article  XIV,  page  204. 

Taking  an  Observation — Locate  the 
sampling  nipple  as  above  directed,  attach  the 
instrument  as  close  to  it  as  possible,  and 


cover  all  exposed  parts  to  prevent  radiation. 
If  the  throttling  calorimeter  be  used,  locate 
the  steam  gauge  on  the  pressure  side,  and  the 
thermometer  on  the  expansion  side.  To 
take  an  observation,  note  simultaneously  the 
gauge  reading  and  the  thermometer  reading, 
and  from  these  the  content  of  moisture  may 
be  determined  directly  from  Fig.  15  or  by 
use  of  formula  [7].  If  the  separating  calori- 
meter be  used,  attach  to  the  separator  outlet 
a  piece  of  hose  which  terminates  in  a  vessel  of 
water  on  a  platform  scale  graduated  to  read 
to  j^  of  a  pound.  Similarly  connect  the 
steam  outlet  to  another  vessel  of  water  resting 
on  an  equally  sensitive  scale.  Note  in  each 
case  the  weight  of  each  vessel  including  the 
water  it  contains.  When  ready  to  take 
an  observation,  blow  out  the  instrument 
thoroughly,  so  there  will  be  no  water  in  the 
separator.  Then  simultaneously  close  the 
separator  drip  and  insert  the  steam  hose  into 
its  vessel  of  water.  When  the  separator  has 
accumulated  a  sufficient  quantity  of  water, 
close  the  valve  at  the  main  steam  pipe,  thus 
cutting  off  the  supply  of  steam  to  the  instru- 
ment, remove  the  steam  hose  from  the  vessel 
of  water  into  which  it  was  inserted,  and 
empty  the  separator  water  into  its  vessel  on 
the  scale.  Note  the  final  weight  of  each 
vessel  and  contents,  then  the  differences 
between  final  and  original  weights  will  be  re- 
spectively, the  weight  of  moisture  collected 
by  the  separator,  and  the  weight  of  steam 
from  which  this  moisture  was  taken,  hence 
the  proportion  of  moisture  can  be  computed 
from  formula  [9]. 

Before  taking  any  calorimeter  observations, 
steam  should  be  allowed  to  flow  through 
freely  until  the  instrument  is  thoroughly 
heated  up. 


Flow  of  Steam  Through  Pipes  and  Orifices 


Formulas  for  the  flow  of  steam  through 
pipes  are  based  upon  Bernoulli 's  theorem  for 
the  flow  of  water  through  circular  pipes  with 
friction,  modified  by  inserting  the  proper 
constants  for  steam.  The  loss  of  energy  due 
to  friction  is  given  by  Unwin  (from  Weis- 
bach)  as 

* 

[10] 


If  D  represents  the  density  or  weight 
of  steam  per  cubic  foot,  and  p  the  loss  of 
pressure  in  pounds  per  square  inch,  due 
to  friction,  then  •,  -r\ 

P  =  [14] 

144 

and  from  [n],  [13]  and  [14], 


where  E  is  the  energy  loss  in  foot  pounds,  due  Let  dj=diameter  of  pipe  in  inches=i2d. 
to  the  friction  of  W  units  (of  weight)  of  Let  w=the  flow  in  pounds  per  minute, 
steam  passing  through  a  pipe  d  feet  in  ( d  )  z  o  6w 

diameter  and  L  feet  long,  with  a  velocity  of     then?f=6oi>X£ -I  —  \  D,  hence  v  =  —     —which 

(12)  *0*D 

TABLE  19 
FLOW    OF    STEAM    THROUGH    PIPES 


Initial  Gauge 

DIAMETER*    OF  PIPE  IN  INCHES.                LENGTH  OP  PIPE   =    240  DIAMETERS. 

Pressure, 
Pounds  per 

* 

I 

li 

2 

ij 

3 

4 

5 

6 

8 

to 

12 

15 

18 

Square  Inch. 

WEIGHT  OF  STEAM  PEH  MINUTE,  IN  POUNDS,  WITH  ONE  POUND  LOSS  OF  PRESSURE. 

i 

I  .16 

2.07 

5-7 

10.  27 

15-45 

25.38 

46.85 

77-3 

H5-9 

211  .4 

34i  •  i 

502.4 

804 

1177 

10 

I  .44 

2-57 

7-1 

12.72 

19-15 

31  -45 

58.05 

95-8 

143.6 

262  .  o 

422.7 

622.5 

996 

1458 

20 

1.70 

3-02 

8.3 

14-94 

22.49 

36.94 

68.20 

112.  6 

168.7 

307-8 

496.5 

731-3 

1170 

1713 

30 

1.  91 

3.40 

9-4 

16.84 

25.35 

41  .63 

76.04 

126.9 

190.  i 

346.8 

559-5 

824.1 

1318 

1930 

40 

2.  10 

3.74 

10.3 

iS.SI 

27.87 

45-77 

84.49 

139-5 

209  .0 

381.3 

6i5.3 

906.0 

1450 

2122 

5° 

2.  27 

4.04 

II  .  2 

20.  OI 

30.13 

49-48 

91  -34 

150.8 

226.0 

412.  2 

665.0 

979-5 

1567 

2294 

60 

2.43 

4.32 

II.  9 

21.38 

32.19 

52.87 

97.60 

161  .  i 

241  .  > 

440.5 

710.6 

046.7 

1675 

2451 

70 

2-57 

4.58 

12  .6 

22.65 

34-10 

56.00 

03.37 

170.7 

255-8 

466  .  5 

752.7 

108.5 

1774 

2596 

80 

2.71 

4.82 

13-3 

23.82 

35.87 

58.91 

08.74 

179-5 

269.0 

490.7 

791.7 

166.1 

1866 

2731 

90 

2.83 

5.04 

13.9 

24.92 

37-52 

61  .62 

13.74 

187.8 

281.4 

513-3 

828.1 

219.8 

I95i 

2856 

IOO 

2.95 

5.25 

14.5 

25.96 

39-07 

64.18 

18.47 

195-6 

293-1 

534.6 

862.6 

270.  i 

2032 

2975 

I2O 

3.16 

5.63 

15.5 

27.85 

41  -93 

68.87 

27  .  12 

209.9 

314.5 

573-7 

925.6 

363.3 

2181 

3193 

ISO 

3.45 

6.  14 

17.0 

30.37 

45-72 

75-09 

38.61 

228.8 

343-0 

625.5 

1009.  2 

486.5 

2378 

3481 

v  feet  per  second;  g  represents  the  accelera- 
tion of  gravity  (32.2)  and  /  the  coefficient 
of  friction,  which  varies  with  the  velocity 
to  a  certain  extent,  and  with  the  size  of  the 
pipe.  Some  authorities  consider  both  of 
these  considerations  negligible  and  treat  / 
as  a  constant.  In  this  article  it  will  be 
regarded  as  varying  according  to  the  size  of 
the  pipe  only,  that  is, 

/-^(i  +  ifa)  ["I 

which  relation  was  established  by  Unwin  for 
a  velocity  of  100  feet  per  second.  K  is  a 
constant  experimentally  determined  and  d 
the  diameter  of  the  pipe  in  feet. 

If  h  be  the  loss  of  head  in  feet,  then 


when  substituted  in  [15]  gives 

f        •?  6  )  wsL 
p  =  0.04839  K \  i  +  —  \ 


The  following  experimental  determinations 

of  K  have  been  made: 

K= .  005  for  water.  (Unwin) 
=  .005    for  air.      (Arson) 
= .  0028  for  air.      (St.  Gothard  Tunnel  Exp.) 
= .  0026  for  steam.  (Carpenter,  Oriskany) 
=  .0027  for  steam.  (G.  H.  Babcock) 

Using  the  value  K=.OO27,  and  substitut- 
ing in  [16]  gives 

3.6)  w*L 
p=o.  000131  ' 


Hence  iv=  87 


[18] 


*Diametets  up  to  5  inches  inclusive  are  actual  internal  diameters  of  standard  pipe,  per  Table  61 ,  p.  213. 

87 


500    H.   P.  OF   STIRLING    BOILERS,  HONOLULU    BREWING   &   MALTING   CO.,  LT'D.,  HONOLULU,  H. 


RESISTANCE    OF    ELBOWS   AND    GLOBE    VALVES 


89 


in  which   w=the  flow  in  pounds  per  minute . 

p  =difference     in   pressure  between 

the  two   ends  of  the    pipe,    in 

pounds  per  square  inch. 

D=density,   or     weight,    per   cubic 

foot  of  steam. 

d,  =diameter  of  pipe  in  inches. 
L=length  of  pipe  in    feet. 
Table   19    is    based    on    formula    [18]  and 
gives    approximately    the    weight    of    steam 
per    minute    which    will    flow    from    various 
initial    pressures,    with    one    pound    loss    of 
pressure,    through    straight,    smooth    pipes, 
each  having  a  length  of  240  diameters. 


For   any   assumed    pipe   length   and   loss, 
the     weight     will    be 


Example:  Find  the  weight  of  steam 
of  100  Ibs.  initial  gauge  pressure  which  will 
pass  through  a  6"  pipe  720  feet  long  with  a 
drop  of  4  Ibs.  Under  the  conditions  in  the 
Table,  293.1  Ibs.  will  pass,  hence  Q  =  293.1 

j  240X6X4  )  * 
and  Q,  =293.  H-   —  —  -  \  =239.3  Ibs 


720X12 

Table  20  is  due  to  Mr.  E.  C.  Sickles,  who 
used    formula     [16]    with    Prof.    Carpenter's 


TABLE  20 
FLOW    OF    STEAM    THROUGH    PIPES 

LENGTH  OF  PIPE  ONE  THOUSAND  FEET 


DISCHARGE  IN  POUNDS  PER  MINUTE  CORRESPONDING  TO  DROP   IN 
PRESSURE  ON  RIGHT  FOR  PIPE    DIAMETERS 

DROP  IN  PRESSURE   IN    POUNDS    PER   SQUARE    INCH  CORRESPOND- 
ING   TO    DISCHARGE  ON    LEFT;    DENSITIES    AND  CORRES- 

IN INCHES  IN  TOP  LINE. 

PONDING    ABSOLUTE  PRESSURES   PER  SQUARE 

INCH  IN  FIRST  TWO  LINES. 

Diameter.- 

12" 

10" 

8" 

6" 

4" 

3" 

2*" 

2" 

ii* 

I- 

Density. 
Pressure. 

.208 
90 

.  230 

100 

.284 
125 

.328 
150 

.401 
1  80 

-443 
200 

.506 

230 

•  548 
250 

Discharge 

2328 

443 

799 

371 

123- 

55-9 

28.8 

8.1 

6.  Si 

•52 

Drop 

18.10 

16.4 

13-3 

ii  .  i 

9-39 

8.50 

7-44 

6.87 

2165 

341 

742 

344 

114.  6 

51-9 

27  .  6 

6.8 

6.52 

-34 

15.60 

14-1 

II.  4 

9.  60 

8.09 

7-33 

6.41 

5-92 

1996 

237 

685 

318 

106. 

47  -9 

26.4 

5-5 

6.  24 

.16 

13-3 

12.  O 

9-74 

8.18 

6.90 

6.  24 

5-47 

5-05 

1830 

134 

628 

292 

97.0 

43-9 

25.2 

4.2 

5-95 

.98 

ii  .  i 

IO.O 

8.13 

6.83 

S.76 

5-21 

4-56 

4-21 

1663 

°3i 

571 

265 

88.2 

39-9 

24.0 

2-9 

5-67 

.80 

9.25 

8.36 

6.78 

5.69 

4.80 

4-34 

3.80 

3-51 

1580 

979 

542 

252 

83.8 

37-9 

22.8 

2.3 

5-29 

•71 

8.33 

7-53 

6.  io 

5.13 

4-32 

3-91 

3-42 

3.i6 

1497 

928 

Si4 

239 

79-4 

35-9 

21.6 

1.6 

5.00 

.62 

7.48 

6.76 

5.48 

4.  60 

3-88 

3-Si 

3-07 

2.84 

1414 

876 

48s 

226 

75- 

33.9 

20.4 

0.9 

4.72 

-53 

6.67 

6.03 

4.88 

4.  io 

3.46 

3-13 

2.74 

2.53 

1331 

825 

457 

212 

70.6 

31-9 

19.2 

0.3 

4-43 

•  44 

5-91 

5-35 

4-33 

3-64 

3-07 

2.78 

2.43 

2.24 

1248 

873 

428 

199 

66.2 

23-9 

18.0 

9.68 

4-15 

•  35 

5-19 

4.69 

3-8o 

3-io 

2.69 

2.44 

2.13 

1.97 

1  164 

722 

400 

1  86 

61.7 

27.9 

16.8 

9-03 

3-86 

.26 

4-52 

4.09 

3-31 

2.78 

2.34 

2.12 

1.86 

1-72 

1081 

670 

37i 

172 

57-3 

25-9 

iS-6 

8.38 

3.68 

•  '7 

3-9° 

3-53 

2.86 

2.40 

2  .02 

1.83 

i  .60 

1.48 

908 

619 

343 

1  59 

52.9 

23-9 

14-4 

7-74 

3-40 

.08 

3-32 

3  -oo 

2.43 

2.04 

I  .72 

1.56 

1.36 

1.26 

9IS 

567 

314 

146 

48.5 

21.9 

13-2 

7.10 

3  -ii 

0.99 

2.79 

2.52 

2.04 

1-72 

i  -45 

I  -31 

i  .'5 

1  .06 

832 

516 

286 

132 

44-  I 

20.0 

12  .0 

6.45 

2.83 

o  .90 

2.31 

2  .OQ 

1  .69 

1.42 

I  .  20 

I  .08 

•949 

.877 

748 

464 

257 

119 

39-7 

18.0 

io..  S 

5-8i 

2.55 

0.81 

1.87 

I  .  69 

1-37 

i.  IS 

-97 

.878 

.769 

.710 

665 

412 

228 

1  06 

35-3 

16.0 

9.6 

5.i6 

2.  26 

0.72 

1-47 

I  -  33 

i  .08 

•  905 

.762 

.690 

.604 

•  558 

582 

36i 

200 

92.8 

3°-9 

14.0 

8.4 

4-52 

1.98 

0.63 

1.  13 

I  .02 

.828 

.695 

.586 

•531 

•  4S6 

.429 

To  get  the  pressure  drop  for  lengths  other  than  1,000  feet,  multiply  by  lengths  in  feet-ri.ooo. 


To  apply  the  table  when  the  pipe  lengths 
and  the  loss  in  pressure  differ  from  those 
assumed,  let  L  =  the  length,  and  d  =  ihe 
diameter  of  pipe,  both  in  inches;  I  =  the 
loss  in  pounds;  Q  =  the  weights  as  given 
in  the  table,  and  Qt  =  the  weight  under 
the  changed  conditions,  then: 

For  any  length  of  pipe,  if  the  weight  of 
steam  passing  is  the  same  as  given  in  the 
table,  the  loss  will  be 


/=. 


240^ 


[19] 


If  the  pipe  length  is  the  same  as  assumed 
in  the  table,  but  the  loss  is  different,  then 
the  quantity  passing  will  be 


=  Ql 


value  K  =0.0026.  To  use  the  table,  assume 
a  certain  drop  in  pressure.  Look  for  this 
drop  in  the  column  at  the  right  under  the 
heading  "Drop  in  pressure  in  pounds;" 
next  pass  to  the  left  along  a  horizontal 
line,  until  under  heading  "Discharge  in 
pounds  per  minute"  the  tabular  quantity 
which  corresponds  nearest  to  the  quantity 
desired,  is  found;  the  size  of  pipe  given  at 
the  top  of  the  column  in  which  the  tabular 
quantity  is  located  will  be  the  one  required. 
Elbows,  globe  valves,  and  a  square  ended 
entrance  to  the  pipe,  all  offer  resistance  to 
the  passage  of  the  steam;  it  is  convenient 
to  consider  this  resistance  equivalent  to  a 
length  of  straight  pipe,  and  add  these  equiv- 
alent lengths  to  the  straight  portions  of 


90 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


the  pipe  line  to  obtain  the  total  length  to 
be  used  in  the  formulas.  Complicated  for- 
mulas for  determining  the  equivalent  length 
have  been  worked  out,  but  in  view  of  the 
varying  proportions  of  valves  and  fittings 
such  formulas  are  not  worth  the  time  it 
takes  to  apply  them,  and  for  all  practical 
purposes  it  will  be  sufficiently  accurate  to 
allow  for  resistance  at  the  entrance  of  a 
pipe  a  length  equal  to  60  times  the  diameter; 
for  a  right  angled  elbow  a  length  of  40  di- 
ameters, and  for  a  globe  valve  a  length  equal 
to  60  diameters. 


the  pipe  to  6,000  ft.  per  minute.  When 
the  pipes  are  long,  this  sometimes  gives 
a  greater  drop  in  pressure  than  is  desirable, 
and  it  is  then  best  to  check  the  sizes  by  refer- 
ring to  the  tables. 

In  marine  work,  a  velocity  of  9,000  ft. 
per  minute  in  steam  pipes  is  very  often 
used  with  excellent  results,  and  there  is  no 
reason  why  this  cannot  be  done  in  stationary 
practise,  provided  the  boilers  can  be  worked 
at  a  pressure  sufficient  to  compensate  for 
the  drop  in  the  pipe  line.  See  the  chapter 
on  Steam  Piping,  page  213. 


TABLE    21 
FLOW  OF  STEAM  INTO  THE  ATMOSPHERE 


Absolute  Initial 
Pressure 
per  Square  Inch. 
Pounds  . 

Velocity  of  Outflow 
at 
Constant  Density, 
Feet  per  Second.* 

Actual  Velocity 
of  Outflow, 
Expanded  . 
Feet  per  Second. 

Discharge 
per  Square  Inch  of 
Orifice  per  Minute. 
Pounds. 

Horse-Power 
per  Square  Inch 
of  Orifice  if  H.P.= 
30  Ibs.  per  Hour. 

25-37 

863 

1,401 

22.  8l 

45-6 

3°- 

867 

1,408 

26.84 

53-7 

40. 

874 

1,419 

35-i8 

70.4 

5°- 

880 

1,429 

44.06 

88.1 

60. 

885 

J,437 

52-59 

105.2 

70. 

889 

i,444 

61  .07 

122  .  I 

75- 

891 

i,447 

65-3° 

130.6 

90. 

895 

i,454 

77-94 

r55-9 

IOO. 

898 

!,459 

86.34 

172.7 

«$• 

902 

1,466 

98.76 

J97-5 

135- 

906 

i,472 

115.61 

231.2 

*55- 

910 

1,478 

132.21 

264.4 

165- 

912 

1,481 

140.46 

280.9 

2I5- 

919 

i,493 

181.58 

363-2 

Drop  in  pressure  in  a  steam  pipe  does 
not  necessarily  indicate  a  loss  of  energy, 
because  the  friction  which  causes  the  drop 
transforms  the  energy  into  heat,  and  this 
evaporates  moisture  and  superheats  the 
steam.  The  superheating  effect  is  very 
slight  ordinarily,  but  will  be  very  manifest 
if  the  pressure  drop  is  large,  as  illustrated 
in  the  throttling  calorimeter. 

A  common  rule  in  laying  out  piping  is 
to  limit  the  velocity  of  the  steam  through 


Flow  of  Steam  into  the  Atmosphere — 

When  steam  is  discharged  into  the  atmos- 
phere, the  velocity  of  outflow  (at  constant 
density  and  when  the  absolute  pressures  are 
greater  than  1.73  times  the  atmospheric 
pressure)  is  as  given  in  Table  21. 

The  external  pressure  per  square  inch  has 
been  taken  as  that  existing  under  the  standard 
atmospheric  pressure  of  14.7  Ibs.  absolute — 
while  the  ratio  of  expansion  in  the  nozzle 
itself  has  been  taken  as  1.624. 


*/.  e.,  if  the  steam  maintained  the  same  density  as  it  had  at  the  initial  pressure. 


FLOW    OF    STEAM   THROUGH    ORIFICES 


91 


Napier's  approximate  formula  for  the  out- 
flow of  steam  into  the  atmosphere  is 

t>& 

Pounds  of  steam  per  second  =  —          [2  2 1 

70 

In  which  p  =  absolute  pressure  in  pounds 
per  square  inch,  and  a  =  area  of  orifice  in 
square  inches.  This  formula  gives  results 
which  correspond  very  closely  with  those  in 
Table  21  as  shown  below: 


f 

Discharge,  Pounds,  per  Minute. 

By 

Table  21. 

By 
Napier's  Rule. 

25-37 

22.81 

21.74 

40. 

35-18 

34-29 

60. 

52-59 

5J-43 

75- 

65-30 

64.29 

100. 

86.34 

85-71 

135- 

115.61 

H5-71 

165. 

140  .  46 

141-43 

2I5- 

181.58 

184.  29 

Prof.  Peabody  conducted  a  series  of  ex- 
periments on  flow  of  steam  through  tubes 
|-inch  in  diameter  and  £-inch  to  ^-inch,  and 
i^-inch  long,  with  rounded  entrances,  in 


which  the  results  agreed  closely  with  Napier's 
formula,  the  greatest  difference  being  an 
excess  of  the  experimental  over  the  cal- 
culated result,  of  3.2  per  cent. 

Flow  of  Steam  from  Orifices  into  a 
Pressure  Above  that  of  the  Atmosphere — 
The  flow  of  steam  of  a  higher  towards  a  lower 
pressure  increases  as  the  difference  of  pressure 
is  increased,  until  the  external  pressure  be- 
comes only  58  per  cent,  of  the  absolute  initial 
pressure.  Below  this  point,  the  flow  of  steam 
is  neither  increased  nor  diminished  by  a  re- 
duction of  external  pressure,  even  to  the  ex- 
tent of  a  perfect  vacuum.  Table  22,  selected 
from  Mr.  Brownlee's  data,  illustrates  this  fact. 
The  following  formula  is  frequently  used 
to  determine  the  flow  of  steam  through  an 
orifice  against  a  pressure  greater  than  two- 
thirds  the  discharge : 

W=i.9  AK(P-p)*  p  [23] 

where  VF=weight  of  escaping  steam  in  pounds 

per  minute. 

A=&rea  of  orifice  in  square  inches. 
K=o.g3  for  a  short  pipe  and  0.63  for 
an  opening  such  as  a  hole  in  a 
plate  or  a  safety  valve. 
P  =  absolute  pressure  of  steam,  pounds. 

per  square  inch. 

p  =  difference  in  pressure  between  the 
two  sides  in  Ibs.  per  square  inch. 


TABLE  22 
FLOW  OF  STEAM  THROUGH   ORIFICES    (Brownlee) 


Absolute  Pres- 
sure in  Boiler 
per  Sq.  In. 
Pounds. 

Absolute 
External  Pressure 
per  Square  Inch. 
Pounds. 

Ratio  of 
Expansion  in 
Nozzle. 

Velocity  of  Out- 
flow at  Constant 
Density. 
Feet  per  Second  . 

Actual  Velocity 
of  Outflow 
Expanded  . 
Feet  per  Second. 

Discharge  per 
Square  Inch  of 
Orifice  per  Min. 
Pounds  . 

75 

74 

I  .012 

227.5 

230. 

16.68 

75 

72 

i-°37 

386.7 

401  . 

28.35 

75 

70 

1.063 

49°- 

521. 

35-93 

75 

65 

1.136 

660. 

749- 

48.38 

75 

61  .62 

1.198 

736. 

876. 

53-97 

75 

60 

i  .  219 

765- 

933- 

56.12 

75 

5° 

1-434 

873. 

1252. 

64- 

75 

45 

1-575 

890. 

1401  . 

65.24 

75 

43-46 

i  .  624 

890.6 

1446.5 

65-3 

75 

IS 

i  .624 

890.6 

1446.5 

65-3 

75 

o 

i  .624 

890.6 

1446.5 

65-3 

FIG.   18.     THE   STIRLING    SUPERHEATER    BOILER  AS    INSTALLED    FOR  THE   GENERAL   ELECTRIC   CO. 
16,000    H.  P.  OF  STIRLING    BOILERS    OPERATED   BY  THIS   COMPANY 


Superheated  Steam  and  the  Stirling  Superheater 


Superheated  steam  is  steam  whose  tem- 
perature exceeds  that  of  saturated  steam  of 
the  same  pressure,  and  it  is  produced  by 
adding  additional  heat  to  saturated  steam 
which  has  been  removed  from  contact  with 
the  water  from  which  it  was  formed.  Its 
properties  approximate  those  of  a  perfect 
gas,  and  its  thermal  conductivity  is  lower 
than  that  of  saturated  steam. 

Superheated  steam  is  used  because : 

(1 )  There  is  always  a  loss  of  heat  by  radia- 
tion from  steam  pipes,  and  the  heat  so  lost  rep- 
resents an  equivalent  condensation  when  the 
pipe  conveys  saturated  steam.     Superheated 
steam  cannot  condense;  it  must  first  lose  all 
of  its  superheat  and  be  reduced  to  saturated 
steam.     In  consequence,  if  sufficiently  super- 
heated it  can  lose  the  amount  of  heat  repre- 
sented by  radiation  from  the  steam  pipes,  yet 
reach    the    engine    perfectly  dry.    Since    the 
thermal  conductivity  of  superheated  steam  is 
less  than   that  of   saturated  steam,  the  heat 
will  not  be  so  rapidly  transmitted   from  the 
body  of  the  steam  to  the  walls  of  the  pipe. 

(2)  In  an  engine  the  steam  is  admitted  into 
a  space  which  has  been  cooled  by  the  steam 
exhausted  during  the  previous  stroke.     The 
heat  necessary  to   warm   the   cylinder  walls 
from  the  exhaust   temperature   to   the   tem- 
perature of  the  entering  steam  can  be  sup- 
plied only  by  the  entering  steam,  hence  if  it 
be  saturated  some  of  it  must  condense.     The 
amount  thus  condensed  is  seldom  less  than 
20  to  30  per  cent,  of  the  total  weight  of  steam 
entering  the   cylinder.      It  is  obvious,   how- 
ever, that  if  an  amount  of  heat  more  than 
sufficient  to  warm  the  cylinder  walls  could, 
by  means  of  superheating,  be  imparted  to  the 
steam  before  it  reached  the  engine,  then  even 
after  the  cylinder  walls  had  been  warmed  up 
the   steam  would  remain  dry,  and  the  initial 
condensation  would  thus  be  overcome. 

These  properties  of  superheated  steam 
have  long  been  known,  but  their  practical 
application  has  been  slow,  owing  to  con- 
structive difficulties.  The  recent  successful 
development  of  the  steam  turbine,  and  of 
reciprocating  engines  adapted  to  the  use  of 
superheated  steam,  has  rendered  necessary 


the  development  of  a  simple,  durable,  effi- 
cient and  safe  steam  superheater.  The 
Stirling  Company  therefore  inaugurated  an 
exhaustive  series  of  researches  and  experi- 
ments on  superheated  steam,  and  these  have 
resulted  in  the  development  of  a  superheater 
which  has  produced  a  higher  degree  of  super- 
heat than  has  yet  been  recorded  as  obtained 
from  any  other  type  of  superheater  installed 
in  connection  with  a  boiler.  In  addition 
to  this,  its  constructive  features  are  as 
radical  an  improvement  over  previous  super- 
heaters as  the  Stirling  boiler  is  over  the  types 
of  boiler  which  preceeded  it. 

Before  describing  the  Stirling  superheater 
the  principles  governing  the  amount  of  super- 
heating surface,  and  of  the  heating  surface 
of  the  boiler  to  which  the  superheater  is 
attached,  will  be  explained  and  illustrated. 

Specific  Heat  of  Superheated  Steam — 
The  amount  of  fuel  required  to  superheat 
steam,  and  the  quantity  of  fuel  that  must  be 
burned  to  produce  this  heat,  are  greater  than 
is  commonly  supposed.  The  specific  heat  of 
superheated  steam  at  atmospheric  pressure 
and  near  the  point  of  saturation  was  found  by 
Regnault  to  be  0.48,  and  for  the  succeeding 
50  years  it  was  thought  that  this  value  of 
the  specific  heat  applied  to  higher  pressures. 
Recent  investigations  both  in  this  country 
and  in  Europe  have  shown  that  the  specific 
heat  is  not  constant,  and  that  it  is  approxi- 
mately 0.65  for  100°  superheat,  and  0.75 
for  200°  superheat.  Using  these  values  it  can 
be  calculated  that  the  fuel  used  to  gen- 
erate saturated  steam  must  be  increased 
by  about  the  following  percentages  in  order 
to  superheat  the  steam  to  the  degrees  named. 

TABLE    23 
FUEL   NEEDED   FOR    SUPERHEATING 


DEGREE  OF 
SUPERHEAT 

75° 
100° 

150° 

200° 
250° 


ADDITIONAL 
FUEL  NEEDED 

•   5% 

7 
ii 

'   '5 

20 


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TEMPERATURE    OF   GASES    SWEEPING   HEATING   SURFACE 


95 


The  degree  of  superheat  being  assumed, 
the  amount  of  superheating  surface  required 
to  produce  it  will  depend  upon  where  the 
surface  is  located  in  the  path  of  the  hot  gases, 
between  the  furnace  and  breeching.  This 
principle  is  of  the  utmost  importance  in  super- 
heater design,  hence  it  will  be  further  illus- 
trated by  means  of  the  curve  in  Fig  19.  In 
this  the  abscissas  represent  the  temperature 
of  the  hot  gases  at  different  points  in  their 
path  from  the  boiler  furnace  to  the  breeching ; 
the  column  on  the  extreme  left  indicates  the 
per  cent,  of  boiler  heating  surface  passed  over 
by  the  gases,  and  the  adjoining  column  gives 
the  amount  of  steam  generated  by  the  heat 
absorbed  from  the  gases,  this  amount  of 
steam  being  expressed  as  a  per  cent,  of  the 
total  steam  generated  in  the  boiler.  Ex- 
ample: When  the  gases  are  cooled  to  700°, 
they  have  passed  over  60%  of  the  boiler 
heating  surface,  and  the  heat  they  have 
given  up  has  generated  90%  of  the  steam 
which  the  boiler  is  producing. 

In  drawing  the  curve,  10  square  feet  of 
heating  surface  have  been  taken  as  the 
equivalent  of  one  boiler  horse-power*,  in  con- 
formity with  the  usual  practise  of  builders  of 
water- tube  boilers.  The  furnace  temperature 
has  been  assumed  as  2500°  F.,  as  the  result 
of  many  experiments  made  by  this  Company's 
engineers.  The  breeching  temperature  of 
500°.  is  assumed  as  a  fair  average  of  condi- 
tions for  best  economy.  This  temperature 
may  appear  to  be  too  high,  in  view  of  the 
statement  current  in  engineering  literature, 
that  for  each  reduction  of  1 00°  in  the  breeching 
temperature  the  boiler  efficiency  is  increased 
6%.  In  order  that  this  statement  may  be 
true  the  air  supply  per  pound  of  fuel,  the  degree 
of  completeness  of  the  combustion,  the  losses 
by  radiation  and  air  leakages,  the  kind  of 
fuel,  and  other  factors,  must  remain  un- 
changed— a  requirement  which  cannot  be 
met  in  practise.  A  deficient  air  supply  will 
cause  the  volatile  matter  in  the  fuel  to  pass 
off  unburnt,  and  while  this  may  lower  the 
breeching  temperature,  it  lowers  the  efficiency 
also.  In  consequence  of  these  facts,  and  as 
further  proved  by  many  tests,  a  low  breeching 
temperature  does  not  necessarily  indicate  high 
efficiency,  and  an  increase  in  the  temperature 
often  augments  the  efficiency,  hence  the 
temperature  of  500°  assumed  in  computing 

*See  definition,  page  195. 


the  curve  is  very  nearly  that  which  gives  the 
best  results  under  average  conditions. 

The  curve  connecting  the  furnace  and 
breeching  temperatures  was  plotted  from  an 
equation  based  upon  the  assumption  that  the 
heat  transferred  from  the  gases  to  the  water 
is  directly  proportional  to  the  difference  in 
temperature;  that  is,  if  the  temperature 
difference  is  1000°,  each  square  foot  of  surface 
will  absorb  twice  as  much  heat  as  it  would 
with  a  temperature  difference  of  500°.  This 
was  the  original  assumption  of  Rankine,  and 
while  its  accuracy  was  later  questioned,  many 
hundred  temperature  measurements  at  differ- 
ent points  along  the  path  of  the  gases  in 
Stirling  boilers  conform  more  closely  to  this 
curve  than  to  any  other.  The  liability  of 
error  is  greatest  at  the  lower  portions  of  the 
curve  where  the  temperatures  are  highest, 
because  at  these  points  large  quantities  of 
heat  are  transmitted  directly  from  the  glow- 
ing coals  to  the  heating  surface  by  radiation, 
while  farther  along  the  path  of  the  gases  the 
heat  is  transmitted  by  convection.  This 
possible  source  of  error,  does  not,  however, 
effect  either  the  part  of  the  curve  to  be  used 
in  the  following  discussion,  or  the  general 
conclusions  to  be  deduced  from  it. 

In  their  path  through  the  boilers  the  gases 
drop  from  2500°  to  500°,  a  difference  of 
2000°.  If  equal  drops  in  temperature  rep- 
resented equal  amounts  of  heat  given  out  and 
absorbed  by  the  boiler,  then  each  200°  drop 
in  temperature  would  represent  10%  of  the 
total  heat  absorbed  by  the  boiler.  This  is 
not  literally  true,  however,  because  the 
specific  heat  of  the  gases  is  greater  at  high 
than  at  low  temperatures,  but  the  difference 
is  not  sufficient  to  affect  the  important  con- 
clusions to  be  drawn  from  the  curve.  Ac- 
cordingly, to  determine  the  figures  in  the 
second  column  on  the  left  side  of  Fig.  19, 
horizontal  lines  have  been  drawn  for  each  200° 
drop  in  the  gas  temperatures,  and  the  cor- 
responding per  cent,  of  the  total  steam  gener- 
ated, up  to  the  point  where  each  drop  is  noted, 
is  written  in  the  column.  For  example,  when 
the  gas  temperature  has  dropped  to  1500°, 
then  19%  of  the  heating  surface  has  been 
passed  over,  and  50%  of  the  total  output 
of  steam  has  been  generated  by  this  19% 
of  heating  surface.  If  the  gases  were  allowed 
to  escape  at  this  point  instead  of  continuing 


HEATING   SURFACE    REQUIRED    PER    HORSE-POWER 


97 


through  the  boiler,  then  40%  of  the  total 
available  heat  would  have  been  utilized,  and 
the  heating  surface  per  boiler  horse-power 
would  be  3.8  square  feet;  here  and  in  the 
following  part  of  this  article  the  term  horse- 
power refers  to  the  horse-power  of  the 
saturated  steam  boiler,  or  the  saturated 
steam  portion  of  the  superheater  boiler, 
without  reference  to  the  additional  capacity 
represented  by  the  superheater. 

Similarly    the    results   for   other   drops   in 
temperature  can  be  calculated  as  follows : 

TABLE  24 


GAS  TEM- 
PEKATURE. 

HEATING  SUR- 
FACE PASSED 
OVER. 

STEAM 
GENER- 
ATED. 

HEATING   SUR- 
FACE  PER 
H.  !•. 

EFFICIENCY 
OF  BOILER. 

I500° 

iQ# 

50  % 

3.   8   sq.ft. 

40% 

IOOO° 

37 

75 

4-   9 

60 

75°° 

54 

87-5 

6.17 

70 

500° 

100 

I  OO 

10.00 

80 

The  efficiency  of  80%  is  possible  with  large 
boilers  burning  high  grade  coal,  oil,  or  gas. 

Application  of  the  Curve  to  the  Prob= 
lemof  Superheater  Design — A  superheater 
maybe  either  independently  fired,  or  be  placed 
in  the  setting  of  a  boiler  and  absorb  heat 
from  the  furnace  gases  which  sweep  over  its 
surface  on  their  way  through  the  boiler. 
The  latter  form  of  superheater  is  the  one 
most  generally  used,  hence  the  principles 
underlying  the  design  of  this  form  of  super- 
heater will  now  be  explained. 

In  order  that  the  superheater  boiler  may 
develop  the  same  thermal  efficiency  as  the 
standard  boiler  used  for  generating  saturated 
steam,  the  furnace  temperature,  the  breech- 
ing temperature,  and  the  weight  of  flue-gases 
per  pound  of  fuel,  must  be  the  same  for  either 
type  of  boiler.  Assume  that  the  superheater 
is  to  be  located  in  the  rear  of  the  boiler,  and 
that  100°  of  superheat  will  be  required. 
From  Table  23  this  degree  of  superheat  will 
require  7%  more  fuel  than  is  required  to 
generate  an  equal  weight  of  steam.  Re- 
ferring to  the  curve,  Fig.  19,  7%  of  the  total 
heat  absorbed  represents  a  drop  of  tempera- 
ture of  140°,  therefore,  as  the  breeching 
temperature  is  to  remain  unchanged,  the 
gases  must  enter  the  superheater  at  a  tem- 
perature of  1 40°+ 5 oo°= 6 40°.  Locating  this 


temperature  on  the  curve,  it  is  found  to 
correspond  to  a  point  where  68%  of  the  heat- 
ing surface  of  the  boiler  has  been  passed  over 
by  the  furnace  gases.  Consequently  32% 
of  the  boiler  heating  surface  of  the  standard 
boiler  must  be  replaced  by  superheating 
surface  sufficient  to  absorb  7%  of  the  total 
heat  absorbed  by  the  boiler.  The  effect 
of  this  substitution  will  then  evidently  be  a 
reduction  of  7%  in  the  weight  of  saturated 
steam  generated,  and  a  reduction  of  32% 
in  the  heating  surface  of  the  boiler,  so  that 
68%  of  the  heating  surface  of  the  saturated 
steam  boiler  generates  93%  of  the  weight  of 
steam  produced  by  that  boiler,  and  the 
heating  surface  per  boiler  horse-power  will 


be =7-i3  square  feet.     It  is  evident  that 

V  O 

if  more  boiler  heating  surface  per  horse-power 
be  installed,  the  gases  will  be  cooled  to  a 
temperature  below  640°  before  entering  the 
superheater,  in  which  case  the  required  de- 
gree of  superheat  will  not  be  obtained,  hence 
it  at  once  follows  that  the  boiler  heating 
surface  of  a  superheater  boiler  must  be 
proportioned  in  a  different  manner  from  that 
in  a  saturated  steam  boiler,  as  will  more 
clearly  be  developed  later  on. 

Since  the  purpose  of  this  investigation  is 
to  determine  the  relation  between  superheat- 
ing surface,  and  the  heating  surface  of  the 
saturated  steam  portion  of  the  boiler  to  which 
the  superheater  is  connected,  it  is  to  be  under- 
stood that  in  the  remainder  of  this  chapter  the 
term  "boiler  heating  surface"  denotes  the 
heating  surface  of  that  part  of  the  combina- 
tion of  boiler  and  superheater  which  generates 
saturated  steam,  while  the  term  "superheat- 
ing surface"  refers  to  the  surface  which  super- 
heats that  steam  after  it  is  generated. 

If  200°  of  superheat  be  required,  15%  of 
the  total  heat  utilized  must  be  absorbed  by 
the  superheater,  which  will  correspond  to  a 
reduction  of  300°  in  the  gas  temperature; 
this  would  require  50%  of  the  heating  surface 
of  the  saturated  steam  boiler  to  be  replaced 
by  superheating  surface,  and  the  remaining 
50%  of  the  boiler  surface  would  have  a 
capacity  of  85%  of  that  of  the  saturated  steam 

boiler,     hence    would     have— =  5.9   square 

•85 

feet  of  boiler  heating  surface  per  horse- 
power. For  75°  superheat,  25%  of  the  boiler 


SUPERHEATER    BOILERS,    BURNING    CRUDE   OIL,    EDISON    ELECTRIC   COMPANY,  LOS   ANGELES,  CAL,, 
6.OOO    H.   P.   OF    STIRLING    BOILERS  OPERATED    BY   THIS   COMPANY 

98 


LOCATION    OF    SUPERHEATER 


99 


heating  surface  would  be  replaced  by  the  super- 
heater, and  there  would  be  7.9  square  feet 
of  boiler  heating  surface. 

Instead  of  locating  the  superheater  behind 
the  boiler  it  may  be  inserted  at  some  inter- 
mediate point  in  the  path  of  the  gases.  For 
instance,  assume  that  the  superheater  re- 
places three-tenths  of  the  heating  surface  of 
the  standard  boiler,  and  is  so  placed  that 
four-tenths  of  the  amount  of  heating  surface 
of  the  standard  boiler  is  located  ahead  of  the 
superheater,  and  the  other  three-tenths  is 
placed  behind  it.  Then  the  part  of  the  curve 
between  40%  and  70%  in  the  left  hand 
column  will  represent  the  cooling  of  the  gas 
while  passing  over  the  superheater;  the  drop 
of  temperature  will  be  300°,  which  represents 
1 5%  of  the  total  heat  absorbed,  hence  from 
Table  23  the  degree  of  superheat  will  be 
200°.  The  boiler  will  produce  85%  as  much 
steam  as  the  saturated  steam  boiler,  and 
the  boiler  heating  surface  per  horse-power 

is  —  =8.24  square  feet. 

If  100°  superheat  were  required  and  the 
ratio  of  boiler  heating  surface  in  front  of  and 
behind  the  superheater  be  kept  as  in  the 
preceding  case,  the  steam  production  will 
be  7%  less  than  in  the  saturated  steam  boiler, 
and  the  gas  temperature  will  be  reduced  140° 
in  the  superheater.  The  requirements  can 
be  met  by  substituting  superheating  surface 
in  place  of  boiler  heating  surface  between 
the  points  in  the  curve  represented  by  63% 
and  48%  in  the  left  hand  column,  and  the 
boiler  heating  surface  per  horse-power  will 

8  t; 
be  —  =  9.14  square  feet . 

•93 

By  removing  the  superheater  farther  for- 
ward, as  for  instance  on  that  part  of  the 
curve  represented  between  21%  and  32% 
in  the  left  hand  column,  the  steam  production 
would  be  15%  less  than  in  the  saturated 
steam  boiler,  the  reduction  of  gas  temperature 
in  the  superheater  will  be  300°,  the  superheat 
will  be  200°,  and  the  boiler  heating  surface 

per  horse-power  will  be  —     =10.5  square  feet. 

It  will,  however,  be  found  that  in  almost 
the  same  proportion  that  the  boiler  heating 
surface  per  horse-power  is  decreased,  the 
necessary  superheating  surface  will  increase, 
so  that  the  sum  of  the  boiler  heating  surface 


and  superheating  surface  per  boiler  horse- 
power will  be  very  nearly  the  same  for  any 
given  degree  of  superheat. 

From  the  preceding  discussion  it  follows 
that  if  a  saturated  steam  boiler  and  a  super- 
heater boiler  are  to  be  of  identical  fuel 
effiiciency  the  following  laws  will  hold : 

(1)  A  superheater  boiler  must  provide  fewer 
square  feet  of  boiler  heating  surface  per  horse- 
power than  are  required  for  a  saturated  steam 
boiler,   provided  the  superheater  is   located  at 
a  point  where  at  least  2  5  %  of  the  boiler  heating 
surface  is  placed  between  the  superheater  and 
the  furnace. 

( 2 )  The    boiler  heating   surface  per   horse- 
power will  be  decreased  as  the  per  cent,  of  boiler 
heating   surface    in    front    of    the    superheater 
is  increased. 

(3)  The  position  of  the  superheater  remain- 
ing the  same,  the  higher  the  superheat  the  less 
the  boiler  heating  surface  required  per  horse- 
power developed  by  the  boiler  heating  surface. 

It  therefore  follows  that  the  superheater 
may  be  placed  either  in  the  rear  of  all  the 
boiler  heating  surface,  or  at  some  intermediate 
position  with  boiler  heating  surface  ahead 
of  and  behind  it.  In  the  two  cases  the  rela- 
tive amount  of  boiler  heating  and  superheat- 
ing surface  must  vary  if  the  results  are  to 
be  the  same. 

The  kind  of  engine  operated  by  the  steam 
has,  however,  a  vital  bearing  upon  the  loca- 
tion of  the  superheater.  The  engine  may 
be  either  a  steam  turbine,  or  a  reciprocating 
engine  whose  working  parts  are  so  designed 
as  to  permit  the  use  of  superheated  steam. 
For  the  steam  turbine  the  degree  of  super- 
heat is  seldom  less  than  100°,  and  is  usually 
higher,  while  the  maximum  superheat  which 
may  be  used  has  yet  to  be  determined.  In 
a  reciprocating  engine  the  superheat  which 
may  be  used  to  advantage  is  limited  by  the 
design  of  the  working  parts,  and  any  con- 
siderable increase  augments  the  difficulty 
of  lubrication,  and  may  cause  trouble  with 
the  packings,  etc.,  hence  the  superheater 
should  be  so  located  that  when  the  boiler 
is  forced  the  steam  temperature  will  not 
exceed  the  limit  which  is  safe  for  such  an 
engine. 

These  requirements  may  be  met  by  proper- 
ly locating  the  superheater.  If  it  be  placed 
in  the  middle  pass  of  the  boiler  the  close 


100 


THE    STIRLING   WATER-TUBE    SAFETY    BOILER 


proximity  of  the  superheating  surface  and 
the  furnace  will  cause  the  degree  of  super- 
heat to  rise  at  times  much  faster  than  can 
occur  when  the  superheater  is  placed  in 
the  rear  pass.  For  this  reason  the  super- 
heater located  in  the  middle  pass  is  to  be 


Fig.  20  represents  a  vertical  section  of  the 
boiler  and  superheater,  as  arranged  for 
superheats  not  exceeding  100°.  The  super- 
heater is  located  behind  the  boiler  heating 
surface,  and  this  design  is  particularly 
adapted  to  operating  reciprocating  engines. 


.•;••: -.-..  ... 


!•...••••??" 

BBSS 


FIG.  20.     SECTIONAL   SIDE    ELEVATION    OF   STIRLING    BOILER   WITH    SUPERHEATER    IN    REAR   PASS 


preferred  for  operating  steam  turbines  where 
the  superheat  exceeds  100°,  while  one  located 
in  the  rear  pass  is  most  suitable  for  supplying 
steam  to  a  reciprocating  engine. 

The  Stirling  Superheater  Boiler  is  de- 
signed in  conformity  with    these  principles. 


Fig.  21  represents  the  section  used  for 
degrees  of  superheat  exceeding  100°.  The 
superheater  is  placed  between  the  two 
banks  of  boiler  heating  surface,  and  by  prop- 
erly proportioning  the  boiler  heating  and 
superheating  surface,  superheats  up  to  250° 


SUPERHEATER   IN    MIDDLE    PASS 


101 


can  be  obtained.  In  either  case  the  super- 
heater consists  of  two  drums  connected 
by  seamless- drawn  tubes  two  inches  in  di- 
ameter. The  construction  is  identical  with 
that  of  the  standard  design  of  Stirling  boiler, 
and  all  of  the  advantages  of  the  bent  tube 


Flooding  the  Superheater — When  de- 
sired the  superheater  may  be  flooded,  and 
used  to  generate  saturated  steam.  Fig.  22 
shows  the  arrangement  of  flooding  pipe 
which  connects  the  front  steam  drum  with 
the  lower  superheater  drum.  \Ynen  the 


§f*sii&ff&fmwq&i#&  _..-*-—  ••<a^% 

fo-ftr".?--. •'  ;-::"'--:  '      '•:  •--•  ;  * -^:;:&;^:?£^ 

FIG.  21.     SECTIONAL    SIDE    ELEVATION    OF  STIRLING    BOILER  WITH   SUPERHEATER   IN    MIDDLE   PASS 


are  retained.  In  addition  the  joint  between 
the  tube  ends  and  the  drums  is  protected 
from  high  heat  by  a  layer  of  asbestos  cement 
which  rests  upon  the  lower  drum,  or  is  sup- 
ported on  metal  bars  placed  below  the  upper 
superheater  drum. 


superheater  is  used  for  generating  saturated 
steam  the  three  compartments  in  the  upper 
drum  are  thrown  into  communication  by 
suitable  valves  so  that  each  compartment 
can  discharge  its  quota  of  saturated  steam 
into  the  main  pipe. 


102 


THE    STIRLING   WATER-TUBE    SAFETY    BOILER 


The  advantages  of  this  arrangement  are 
obvious.  The  superheater  boiler  may,  in 
emergencies,  be  used  as  a  saturated  steam 
boiler  to  operate  other  engines  in  the  plant 
when  those  which  use  superheated  steam 
are  shut  down.  When  a  number  of  super- 


Course  of  the  Steam  in  the  Super- 
heater— The  upper  drum  in  the  superheater 
is  divided  into  three  compartments  by 
means  of  two  partitions,  and  the  lower 
drum  is  similarly  divided  into  two  com- 
partments; each  partition  either  contains 


FIG.  22.     SIDE   ELEVATION   OF  STIRLING   SUPERHEATER   BOILER,  SHOWING   FLOODING   PIPE 


heater  boilers  are  operated  together,  and 
it  is  desired  to  reduce  the  degree  of  super- 
heat, any  one  of  these  boilers  may  be  used 
to  generate  saturated  steam  only,  and  this 
be  mixed  with  the  superheated  steam  to 
reduce  the  degree  of  superheat  to  any  de- 
sired point. 


a  manhole,  or  is  removable,  so  that  all 
parts  of  the  drum  are  accessible.  The 
steam  enters  one  end  compartment  of  the 
upper  drum,  and  makes  four  passes  through 
the  tubes,  as  indicated  in  Fig.  23. 

Independently  Fired  Superheater — Fig. 
24     represents    the     Stirling     Independently 


REMOVING   TUBES    FROM   SUPERHEATER  BOILER 


103 


Fired  Superheater.  In  this  all  the  con- 
structive advantages  of  the  Stirling  boiler 
are  retained.  The  saturated  steam  from 
the  main  boiler  plant  enters  the  rear  super- 
heater drum,  passes  through  the  rear  bank 
of  tubes  into  the  lower  drum,  thence  to  the 
upper  drum,  from  which  it  passes  into  the 
pipe  line.  The  furnace  is  similar  to  that 
used  in  the  standard  design  of  Stirling 
boiler.  To  protect  the  superheater  tubes 
from  the  high  temperature  of  the  furnace 
a  sufficient  amount  of  boiler  heating  surface 
is  located  in  front  of  the  superheater  to 


FIG.  23.     SECTION  THROUGH  STIRLING  SUPERHEATER, 
SHOWING   PATH  OF  STEAM 

reduce  the  temperature  of  the  gases  to  1500° 
by  the  time  they  reach  the  superheater 
tubes.  Referring  to  the  curve,  Fig.  19,  it 
will  be  noted  that  when  the  gas  temperature 
reaches  1500°  in  the  standard  boiler,  19%  of 
the  boiler  heating  surface  has  been  swept 
over  by  the  gases,  50%  of  the  steam  produced 
by  the  boiler  has  been  generated,  and  the 
boiler  heating  surface  per  horse-power  is 
3.8  square  feet.  Consequently  in  the  in- 
dependently fired  superheater  shown  in 
Fig.  22  50%  of  the  heat  absorbed  is  used 
to  generate  steam  which  is  added  to  the 
steam  furnished  by  the  main  boiler  plant, 


hence  increases  the  capacity  of  the  plant 
in  proportion.  The  remaining  50%  of  the 
heat  is  absorbed  by  the  superheater,  and 
superheats  both  the  steam  from  the  main 
boiler  plant  and  that  from  the  front  bank  of 
water- tubes.  If,  for  example,  the  degree 
of  superheat  is  150°,  then  from  Table  23  it 
will  take  11%  as  much  heat  to  superheat  a 
pound  of  steam  as  to  generate  it  from  water 
in  form  of  saturated  steam,  hence  for  each 
pound  of  saturated  steam  generated  in  the 
front  bank  of  the  superheater,  9T1T  pounds 
may  be  superheated,  and  8j\  pounds  are 
delivered  from  the  boilers,  therefore  the 
superheater  will  generate  about  12%  of 
the  amount  of  steam  furnished  by  the  main 
boiler  plant. 

As  a  further  precaution  against  any 
possible  overheating  of  the  superheater  tubes 
nearest  to  the  furnace,  a  flap  valve  is  placed 
in  the  pipe  conveying  saturated  steam  to 
the  superheater,  as  shown  in  Fig.  24.  The 
spindle  of  this  valve  is  connected  by  links 
to  the  superheater  damper,  so  that  the 
damper  opening  is  regulated  according  to 
the  quantity  of  steam  flowing  into  the  super- 
heater; if  the  steam  flow  stops,  the  valve 
drops  to  its  seat,  and  the  damper  is  closed. 

To  provide  for  circulation  in  the  water- 
tubes,  four  "downcomer"  tubes  are  placed 
at  each  end  of  the  drum,  as  shown  in  the 

section  on  line  A B,  Fig.  24.  These 

are  placed  in  a  slot  in  the  wall  and  are  pro- 
tected from  heat  by  the  tile  as  shown. 

Independently  Fired  Superheaters  can  be 
furnished  of  any  desired  capacity,  suitable 
for  any  superheat  up  to  250°. 

Flooding  Pipe — The  upper  water  drum 
and  lower  superheater  drum  are  connected 
by  piping,  as  shown  in  Fig.  22,  hence,  if 
desired,  the  superheater  sections  may  be 
flooded,  converting  the  whole  into  a  satur- 
ated steam  boiler. 

Removing  Tubes  from  the  Superheater 
Boiler — The  3^-inch  tubes  in  the  boiler 
heating  surface  are  alternately  spaced  6| 
and  5^  inches;  the  2-inch  superheater  tubes 
are  alternately  spaced  4^  and  3  inches. 
See  Fig.  12.*  This  method  of  spacing  per- 
mits any  tube  to  be  removed  from  the  drums 
and  be  passed  through  the  wider  spacing, 
hence  any  tube  in  the  boiler  or  superheater 
can  be  replaced  without  disturbing  other  tubes. 


104 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


Cleaning — An  extremely  important  ad- 
vantage is  that  the  superheater  tubes  may 
be  cleaned  by  means  of  a  turbine  cleaner 
in  precisely  the  same  manner  as  the  regular 
boiler  tubes  are  cleaned.  This  point  is  of 
the  utmost  importance,  since  when  using 
feed  waters  containing  vegetable  matter, 


vision  is  made  for  flooding  the  superheater 
and  using  it  in  emergencies  to  generate 
saturated  steam,  it  is  evident  that  for  sat- 
isfactory service  it  is  necessary  that  the  super- 
heater tubes  be  just  as  readily  cleaned  as 
the  water  tubes.  This  requirement  is  per- 
fectly met  in  the  Stirling  superheater. 


SATURATED  STEAM  FROM  BOILER  PLANT 


SUPERHEATED  STEAM 


FIG.  24.     SECTIONAL   SIDE    ELEVATION    OF  THE   STIRLING    INDEPENDENTLY   FIRED   SUPERHEATER 


sewage,  etc.,  some  of  this  matter  will  be 
carried  over  into  the  superheater  and  de- 
posited upon  the  tubes,  hence  no  form  of 
superheater  that  cannot  be  readily  cleaned 
will  meet  the  requirements  of  successful 
use,  considered  as  a  superheater  only.  When, 
as  in  case  of  the  Stirling  superheater,  pro- 


Superheaters  for  Boilers  already  In- 
stalled— The  Stirling  Company  manu- 
factures superheaters  which  may  be  attached 
to  any  Stirling  boiler  now  in  use,  and  will 
promptly  furnish  blue  prints,  prices,  and 
full  information  on  application  from  pros- 
pective purchasers. 


Combustion 


Combustion,  as  the  term  is  used  in  steam 
engineering,  is  the  rapid  chemical  combi- 
nation of  oxygen  with  carbon,  hydrogen  and 
sulphur,  with  the  accompaniment  of  heat 
and  light.  The  substance  which  combines 
with  the  oxygen  is  the  combustible.*  The 
combustion  is  perfect  when  the  combustible 
is  oxidized  to  the  highest  possible  degree; 
thus,  conversion  of  carbon  into  carbon 
dioxide  (C02)  represents  perfect  combustion, 
while  its  conversion  to  monoxide  (CO)  is 
imperfect  combustion,  since  the  monoxide 
can  be  further  burned  and  finally  converted 
into  COS . 

Kindling  Point — As  in  many  other  chem- 
ical processes,  a  certain  degree  of  heat  is 
necessary  to  cause  the  union  of  the  oxygen 
and  combustible;  the  temperatures  necessary 
to  cause  this  union  are  the  kindling  temp- 
eratures, and  are  approximately  as  given 
in  the  following  table  by  Stromeyer.f 

TABLE  25 
KINDLING  TEMPERATURES 

Lignite  Dust  .      .      .      300°  F. 
Sulphur     .      .      .      .470 
Dried  Peat      .      .      .435 
Anthracite  Dust         .      570 

Coal 600 

Cokes Red  Heat 

Anthracite      .      .      .        "       "75° 
Carbon  Monoxide       .  '1211 

Hydrogen  .  .  .  1030  or  1290 
The  Oxygen  necessary  for  combustion 
is  supplied  from  the  air.  Its  density  is 
1.10521,  (Air  =  i);  its  weight  0.088843  Ibs. 
per  cu.  ft.  at  32°  F.,  and  atmospheric  pressure; 
its  atomic  weight  is  16;  a  pound  of  air  con- 
tains 0.2315  Ibs.  of  oxygen,  and  one  pound 
of  oxygen  is  contained  in  4.32  Ibs.  or  air. 

Carbon  (C),  the  most  abundent  com- 
bustible, has  atomic  weight  of  12,  and  reaches 
the  boiler  furnace  as  a  constituent  of  oil, 
gas,  coal,  charcoal,  wood,  etc. 

Hydrogen  (H)  occurs  free  in  small  quan- 
tity in  some  fuels,  but  is  usually  in  combi- 
nation with  the  carbon.  Its  atomic  weight 
is  i;  its  density  is  0.0692,  (Air=i);  and  its 


weight  per  cubic  foot  at  32°  F.  and  atmos- 
pheric pressure  is  0.00559  Ibs. 

Sulphur  (S,  atomic  weight  32)  is  found 
in  most  coals  and  in  some  oils.  It  is  usually 
present  in  a  combined  form,  either  as  sul- 
phide of  iron,  or  sulphate  of  lime;  in  the 
latter  form  it  has  no  heating  value.  Its 
presence  in  fuel  is  objectionable  because 
the  gases  formed  from  its  combustion  attack 
the  metal  of  the  boiler  and  causes  rapid  cor- 
rosion, particularly  in  presence  of  moisture. 

Nitrogen  (N)  is  drawn  into  the  furnace 
with  the  air.  Its  atomic  weight  is  14;  its 
density  is  0.9701,  (Air=i);  its  weight  per 
cubic  foot  at  32°  F.  and  atmospheric  pressure 
is  .07831  Ibs.;  each  pound  of  air  at  atmos- 
pheric pressure  contains  0.7685  Ibs.  of  nitro- 
gen, and  one  pound  of  nitrogen  is  contained 
in  1.301  Ibs.  of  air. 

Nitrogen  performs  no  useful  office  in  com- 
bustion, and  passes  through  the  furnace 
without  change.  It  dilutes  the  air,  absorbs 
heat  and  reduces  the  temperature  of  the 
products  of  combustion  and  is  the  chief 
source  of  heat  loss  in  furnaces. 

Combining  Weights — When  chemical  el- 
ements unite  to  form  a  new  compound 
they  do  so  in  definite  proportions  which 
are  always  the  same,  and  the  union  produces 
heat  the  quantity  of  which  is  also  invariable. 
Thus,  a  pound  of  carbon,  when  carbon 
dioxide  is  formed,  will  always  unite  with 
2§  pounds  of  oxygen,  and  give  off  14,600 
B.  T.  U.  As  an  intermediate  step  the  carbon 
might  unite  with  i^  times  its  weight  of  oxy- 
gen, and  produce  4,450  B.  T.  U.,  but  in  its 
further  conversion  to  CO2  it  would  unite 
with  an  additional  i£  times  its  weight  of 
oxygen  and  evolve  the  other  10,150  B.  T.  U., 
since  the  heat  developed  in  any  chemical 
combination  depends  upon  the  initial  and 
final  states,  and  not  upon  any  intermediate 
change. 

Calorific  Value  of  Fuel — The  amount  of 
heat  liberated  per  pound  of  fuel  undergoing 
perfect  combustion  is  called  the  calorific  value 
of  the  fuel.  The  methods  of  determining 
the  calorific  value  will  be  treated  in  chapter 
on  Determination  of  Heating  Value  of  Fuels. 


*See  foot-note,  page  112.          ^Marine  Boiler  Management  and  Construction,  page  93. 


106 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


Table  26  gives  calorific  values,  air  required, 
etc.,  for  the  elementary  combustibles  and 
several  compounds. 

Hydrogen  Available  for  Combustion— 

During  complete  combustion  the  carbon 
will  be  converted  into  carbon  dioxide,  (CO2); 
the  hydrogen  into  water  vapor,  (H2O); 
and  the  sulphur  into  gas  of  the  composition 
SO2.  Not  all  the  hydrogen  shown  by  a  fuel 
analysis  is,  however,  available  for  heat  pro- 
duction, since  the  oxygen  shown  by  the  an- 
alysis was  united  with  part  of  the  hydrogen 
in  form  of  water,  hence  was  already  in  com- 
bination before  combustion  was  effected. 
Since  water  is  H2O  and  the  atomic  weights 
of  H  and  O  are  respectively  i  and  16,  the 
weight  of  combined  hydrogen  will  be  one- 
eighth  of  the  weight  of  the  oxygen,  hence 
the  hydrogen  available  for  combustion  will 
beH-iO. 


Carbon  . 
Hydrogen   . 
Oxygen 
Nitrogen 

•      •      74-79% 
.      .       4.98 
6.42 
i  .  20 

Sulphur 
Water    .      .      .      . 
Ash 

3-24 
7.82 

IOO  .  OO% 


Substituting  in  the  formula 

B.  T.  U.  per  pound. = 
14600X0.7479 

(  0.0642 

+62000  4  0.0408- 


+4000X0.0324 

=  13,650,  very  nearly. 

A  calorimeter  test  showed  13480  B.  T.  U. 
for  this  coal,  which  illustrates  the  degree  of 
accuracy  to  be  expected  of  the  formula.  A 
more  refined  computation  would  involve  a 


TABLE  26 
COMBUSTION   DATA  FOR    CARBON,    HYDROGEN,    ETC. 


I 

2 

3 

4 

5 

6 

7 

8 

9 

10 

Oxidizable 
Substance, 
or  Fuel. 

Chem- 
ical 
Symbol 

Atomic 
or  Com- 
bining 
Weight 

Chemical  Reaction. 

Product  of 
Combustion. 

Oxygen 
per  Ib. 
of  Col.  i 

Ibs. 

Nitrogen 
per  lb.- 
of  Col.  i 
=  3.32XO 
Ibs. 

Air  per  Ib. 
of  Col.  i 
=  4.32XO 
Ibs. 

Gaseous 
Product 
per  Ib. 
of  Col.  i 
=  Col.  i  X 
Col.  8.    Ibs. 

Heat 
Value 
per  Ib. 
of  Col.  i 
B.T.  U. 

Carbon 

C 

12 

C+2O=CO2 

Carbon  Dioxide 

2$ 

8.85 

it  .52 

12.52 

14,600 

Carbon 

C 

12 

c+o=co 

Carbon  Monoxide 

l| 

4-43 

5.76 

6.76 

4.4SO 

Carbon  Monoxide 

CO 

28 

CO+O=CO2 

Carbon  Dioxide 

4/7 

i  .90 

2  .47 

3  -47 

IO,I  $O* 

Hydrogen 

H 

I 

2H+O=H2O 

Water 

8 

26.56 

34-  56 

35  .  56 

62,000 

Methane 

CH4 

16 

CH4+4O=CO2+2H2O 

Carbon  Dioxide 

and  Water 

4 

13.28 

17.28 

18.38 

23,5<;o 

Sulphur 

S 

32 

S+2O=SO2 

Sulphur  Dioxide 

i 

3-33 

4.32 

5-32 

4,050 

Dulong's  Formula — The  heating  value 
of  the  various  elements  being  known,  the  fol- 
lowing formula,  due  with  slight  modifications 
to  Dulong,  enables  the  heat  of  combustion 
of  a  fuel  to  be  computed. 

Heating  value  of  fuel   per  pound= 

14,600(7+62,000  •]  H — — -  >  +4,oooS        [24] 
(          8    ) 

C,  H,0,and  5  are  the  proportionate  parts, 
by  weight,  of  carbon,  hydrogen,  oxygen  and 
sulphur,  respectively.  The  formula  does  not 
apply  when  the  fuel  contains  carbon  mon- 
oxide, (CO),  but  can  be  made  to  apply  by 
adding  the  term  10,150  Cf,  in  which  C  is  the 
proportionate  weight  of  carbon  which  is  con- 
verted into  carbon  monoxide. 

Assume,  for  example,  a  coal  whose  com- 
position is  as  follows: 


correction  for  heat  expended  in  evaporating 
the  water  in  the  coal  and  superheating  the 
resultant  vapor  to  the  breeching  temperature. 
Air  Required— From  Table  26  the  air 
required  can  be  readily  calculated, thus: 
0.7479  CX2§  .  .  .  =1.9944  Ibs.  O  needed 

]  0.0498-  °'°  42  [  HX8  =0.3262    "     " 
(  8       ) 

0.03248X1=  .      .      .     =0.0324  ' 

Total  ....     =2.3530  Ibs.  O  needed 
Since   i   pound  of  oxygen  is  contained  in 
4.32  Ibs.  of  air,  the  total  air  needed  will    be 
2.353X4.32=10.165  Ibs.     The  weight  of    act- 
ual combustible  is 

.  7479+. 040775+. 0324=. 82  pounds, 
hence   the   air  required   per  pound   of   com- 
bustible is  10.165-^.82=12.4  Ibs. 


*Per  pound  of  carbon  in  the  monoxide;  the  heat  value  of  a  pound  of  carbon  monoxide  is  4.350  B.  T.  U. 
fOr  by  adding  the  term  4,350  CO  if  the  weight  of  CO  be  known. 


HEAT    LOSSES   DUE    TO    EXCESS    AIR 


107 


The  air  may  be  also  found  by  following 
approximate  formula: 

Weight   of    air  per  Ib.   of  fuel= 

S  [25] 


in  which  the  letters  have  same  significance  as 
in  Dulong's  formula  above  given. 

Table  27  gives  the  air  supply  for  various 
fuels,  calculated  as  above  explained. 

TABLE  27 

CALCULATED  NET  QUANTITY  OF  AIR  REQUIRED 
FOR  COMBUSTION  OF  VARIOUS  FUELS 


FUEL. 

WEIGHT  OF  GIVEN  CONSTIT- 
UENT IN    I    LB.    OF  FUEL. 

POUNDS  OF 
AIR  REQUIRED 

CARBON. 

HYDRO- 

OXYGEN. 

PER  LB.   OF 
FUEL. 

% 

GEN    % 

% 

Wood  Charcoal 

93- 

II.  16 

Peat  Charcoal  . 

So. 

9.6 

Coke       .... 

94- 

11.28 

Anthrarite  Coal 

91-5 

3-5 

2  .  6 

12.13 

Dry  Bituminous  Coal 

87. 

5-0 

4.0 

12.  06 

Lignite  .... 

70. 

5-0 

20  .0 

9-3° 

Dry  Peat     .      .       . 

58. 

6.0 

31.0 

7.68 

Dry  Wood  . 

5°. 

..... 

6.00 

Mineral  Oil 

85. 

15-65 

The  above  values  are  useful  for  comparison 
with  the  air  actually  used  in  any  given  case. 
To  produce  perfect  combustion  with  the 
calculated  quantity  of  air  would  require  that 


resistance  to  passage  through  the  fuel  in 
different  places  owing  to  ash,  clinker,  etc. 
Where  such  difficulties  are  absent,  as  when 
burning  gas  or  oil  fuel,  the  air  supplied  may 
be  materially  less  than  that  required  for  coal. 
Experiment  shows  that  under  either  natural 
or  forced  draft  coal  requires  about  50%  more 
than  the  net  calculated  amount  of  air,  or 
about  1 8  pounds  per  pound  of  coal.  If  less 
is  supplied  the  carbon  burns  to  monoxide 
instead  of  dioxide,  thus  fails  to  develop  its 
full  heat  value.  An  excess  of  air  is  also  a 
source  of  waste,  as  it  dilutes  the  products  of 
combustion,  and  reduces  the  temperature 
by  absorbing  heat  which  is  conveyed  to  the 
breeching.  Table  No.  28  by  Coxe*  indicates 
the  magnitude  of  the  heat  losses  due  to  ex- 
cess of  air  supply.  By  minimum  air  supply 
is  meant  the  net  calculated  quantity, 

Temperature  of  the  Fire — If  the  heat  due 
to  combustion  of  the  fuel  and  the  weight 
and  specific  heat  of  the  products  of  combustion 
be  all  known,  the  temperature  of  the  furnace 
(neglecting  heat  lost  by  radiation  and  con- 
duction) can  be  calculated.  Evidently, 

Heat  of  combustion  in  B.  T.  U= Weight 
of  products  of  combustion  X  their  specific 
heat  X  elevation  of  temperature  of  products 
in  degrees.  [26] 


TABLE  28 

SHOWING    HEAT    LOSSES    WHEN    BURNING    100  POUNDS    OF    ANTHRACITE 
WITH    MINIMUM,  AND  TWICE  THE  MINIMUM  AIR  SUPPLY 

(100  pounds  of  anthracite  are  assumed  equal  to  1,313,080  B.  T.U.     T=chimney  temperature. 
Atmospheric  temperature  assumed  at  60°  F.) 


TOTAL    HEAT    LOST    IN    GASES. 


T=400°. 

T=500°. 

T=6oo°. 

T=700°. 

T=8oo°. 

B.  T.   U. 

% 

B.  T.   U. 

% 

B.  T.   U. 

% 

B.  T.    U. 

% 

B.  T.   U. 

% 

Minimum  Air  Supply 
Twice  Minimum  Air 

145.755 

1  1  .0 

I7I-754 

J3 

!97.753 

15 

223.751 

I7.0 

249,  751 

19  .0 

Supply     .... 

230,097 

J7-5 

279,007 

21 

329,176 

25 

378,715 

28.8 

428,254 

32.6 

each    particle    of    oxygen    be    brought    into  To     illustrate,  assume  that  the  same  coal 

intimate  contact  with  the  fuel.     This  cannot  as  in  last  problem  is  burned  with  the  minimum 

be  done  in  practise,  because  of  the  mixture  supply  of  air.     The   sulphur  and  the   small 

of  the  oxygen  with  nitrogen  in  the  air,  the  quantity  of  oxygen  needed    to  burn    it  may 

irregular  thickness  of  the  fire,   and  varying  be  neglected.     Then: 

*See  Thurston,  Manual  of  Steam  Boilers,  p.  672. 


108 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


Weight  of   CO2  =  . 7479+1. 9944    =2.7423  Ibs, 

Weight     of     H8  0=o. 04077+ 

0.3262 =  .3310     " 

Nitrogen  carried  in  by  10.165 

Ibs.    of  air=io. 165X0. 7685     .    =7.8118 

Total  weight  of  products,  in- 
cluding nitrogen     ....      10.8861 


combustion  with  the  minimum  quantity  of  air, 
such  a  furnace  temperature  cannot  possibly 
be  reached  in  practise.  To  illustrate  the 
diminution  of  furnace  temperature  due  to 
excess  of  air  supply,  the  preceding  case  will 
be  worked  out  on  basis  of  twice  the  minimum 
air  supply.  This  gives  the  following  result: 


TABLE  29 
COOLING  EFFECT  OF  VARIOUS    PERCENTAGES  OF  EXCESS  AIR 


(Based  on  coal  containing  €  =  85$;   £[  =  2.5%;  N  =  i#;  Ash  =  7.75#,  and  B.T.  U.  =  14,  750 
per  pound.     Temperature  of  external  air  =  o°F.) 


TEMPERATURE   OF   COM- 

PER CENT.  OF  AIR  ADDED 

IDEAL  TEMPERATURE 

LOSS  OF  TEMPERATURE 

BUSTION  COMPARED 

TO  THE  MINIMUM 

OF  COMBUSTION. 

DUE  TO  DILUTION. 

WITH  THAT  DEVEL- 

QUANTITY. 

DEGREES. 

DEGREES. 

OPED  BY  MINIMUM 

QUANTITY  OF  AIR. 

o  (or  Minimum  Quantity) 

^,1^2°    F 

10%  Added 

J  '      O 

4,710 

422 

9I.8% 

20 

4,352 

780 

84.8 

3° 

4,044 

1,  088 

78.8 

40 

3-777 

1.355 

73-6 

5° 

3-543 

1,589 

69  .0 

60 

3,336 

1,796 

65.0 

70 

3>I53 

1,979 

61.4 

80 

2,988 

2,144 

58.2 

90 

2,840 

2,292 

55-3 

100 

2,705 

2,427 

52-7 

125 

2,419 

2,7J3 

47-i 

150 

2,188 

2,944 

42  .6 

175 

1,997 

3,I35 

38.9 

2OO 

1,837 

3,295 

35-8 

=  0.59508  B.  T.  U. 


The  mean  specific  heat  of  this  mixture 
being  unknown,  the  heat  necessary  to  raise 
the  mixture  one  degree  will  be  now  calculated. 
2.7423X0.217  (specific 

heatofCO2     .      .      . 
0.3310X0.4805  (specific 

heat  superheated  steam. *=  0.15905 
7.8118X0.2438    (specific 

heat  of  N)       .      .      .      .=  1.90452 

Hence  total  heat  to  raise 

products    one  deg.  F.      =2.65865  B.  T.  U. 

The  calculated  calorific  value  of  this  coal 
was  13650  B.  T.  U.,  hence  the  elevation  of 
temperature  will  be  2]"™K  =  5134°  F.  But 
because  of  the  impossibility  of  getting  proper 


B.  T.  U.  for  minimum  air  supply  as 

already  determined   ....      =2.65865 

Additional  B.  T.  U.  for  10.165  lbs-  of 

air  =10. 165   x  0.2375      •       •       •      =  2.41419 

B.T.  U.  required  to  raise  products  of 
combustion    (including    nitrogen) 

one  degree =5.07284 

Hence  elevation   of  furnace   temperature  = 
F. 


In  the  preceding  computation  the  specific 
heat  of  air  has  been  assumed  as  equal  to 
.2438,  its  value  at  32°F.,  as  is  almost  invar- 
iably done  when  computing  furnace  tem- 
peratures. It  is  known,  however,  that  at 
high  temperature  the  specific  heat  of  air  is 


(*)      Heat  to  raise  the  water  to  boiling  point  is  here  neglected.     The  specific  heat  of  superheated  steam 
is  also  greater  than  here  used.     See  p.  93. 


FUEL   LOSSES   DUE    TO    INCOMPETENT    FIRING 


109 


considerably  greater,  and  while  exact  deter- 
minations have  not  yet  been  made,  enough 
has  been  done  to  show  that  at  the  usual 
furnace  temperatures  the  specific  heat  closely 
approximates  to  0.3.  Assuming  this  value, 
the  preceding  computation  would  give  a 
furnace  temperature  of  2220°  which  is  more 
nearly  correct  than  the  temperature  of  2690° 
previously  found. 


be  burned  only  to  carbon  monoxide,  which 
will  develop  less  than  one-third  of  the  heat 
which  is  produced  when  the  carbon  is  con- 
verted into  carbon  dioxide. 

This  subject  is  of  greatest  practical  im- 
portance, owing  to  the  large  and  usually 
unsuspected  loss  of  fuel  due  to  incompetent 
or  careless  firing.  Large  sums  of  money  are 
often  spent  on  devices  intended  to  save  a  few 


750   H.    P.   OF  STIRLING    BOILERS,    ROBINSON'S   CENTRAL  DEEP,    LIMITED,   SOUTH  AFRICA 


Table  29  further  illustrates  the  cooling 
effect  of  excess  air.  In  practical  work  the 
temperatures  will  be  even  less  than  given  in 
the  table,  because  of  losses  due  to  radiation, 
slicing  fires  and  removal  of  ashes,  and  further 
fact  that  at  high  temperatures  the  specific 
heat  of  gases  is  probably  greater  than  the 
values  for  lower  temperatures,  the  only  values 
at  present  available  for  use  in  making  the 
computation. 

The  temperature  is  also  lowered  by  insuf- 
ficient air  supply  because  the  carbon  will 


per  cent,  of  fuel,  while  through  careful  atten- 
tion by  a  skilled  fireman  much  greater  savings 
could  be  effected  without  any  expense  what- 
ever. The  computations  are  also  valuable 
as  indicating  why  boiler  efficiencies,  when 
gas  or  oil  fuel  is  used,  are  often  ten  to  fifteen 
per  cent,  higher  than  when  burning  coal,  the 
difference  being  due  to  decrease  in  the  excess 
of  air  used,  and  prevention  of  heat  losses  due 
to  hot  ashes,  slicing  fires,  opening  of  fire 
doors,  and  admission  of  cold  air  into  the 
furnace  when  burning  coal. 


OF  THE 

UNIVERSITY 


Fuels  for  Steam  Boilers 


Fuels  may  be  solid,  liquid,  or  gaseous. 
Such  representatives  of  each  class  as  are  used 
for  firing  steam  boilers  will  be  considered. 

Coal  is  the  fossilized  remains  of  prehistoric 
vegetable  growth.  In  its  stages  from  vege- 
table to  almost  pure  carbon  in  the  form  of 
graphite,  it  was  successively  changed  into  the 
forms  listed  in  Table  30.  With  each  stage 
the  content  of  carbon  increases. 

TABLE  30 

APPROXIMATE  CHEMICAL  CHANGES,  WOOD  FIBRE 
TO  ANTHRACITE  COAL 


SUBSTANCE. 

CARBON. 

HYDROGEN. 

OXYGEN. 

Wood  Fibre   .... 

52.65 

5.25 

42  .  10 

Peat    

59-57 

5.96 

34-47 

Lignite      

66  .  04 

5-27 

28.69 

Earthv  Brown  Coal 

73.i8 

5.58 

21.14 

Bituminous  Coal 

75.06 

5.84 

JO  -  JO 

Semi-bituminous  Coal    . 

89.  29 

5-05 

6.66 

Anthracite  Coal  . 

91.58 

3.96 

4.46 

Table  31  gives  the  approximate  per- 
centages of  carbon  and  volatile  matter  in  the 
combustible  portion  of  the  general  classes  of 
coals. 

TABLE  31 

CLASSIFICATION  OF  COALS  ACCORDING  TO  CON- 
STITUENTS IN  THE  COMBUSTIBLE* 


FIXED 

VOLATILE 

CARBON. 

MATTER. 

Anthracite  
Semi-anthracite 
Semi-bituminous    . 

97        t092.5% 
92.5  to  87.5 
87-5  to  75 

3        to     7.5% 

7.5  to  12.5 

12  .5  tO  25 

Bituminous,  Eastern  . 

75       to  60 

2  5          tO  4O 

Bituminous,  Western 
Lignite         

65       to  50 
under     50 

35        to  50 
over   50 

The  percentages  of  ash  and  moisture  in 
coal  vary  greatly.  The  ash  ranges  from  three 
to  thirty  per  cent.,-  and  the  moisture  from 
0.75  to  25  per  cent,  of  the  total  weight  of  the 
coal,  depending  upon  the  locality  where  mined 
and  the  grade. 

Anthracite,  or  Hard  Coal,  ignites  slowly, 
but  when  in  a  state  of  incandescence  its  radi- 
ant heat  is  very  great.  The  name  Anthracite 
may  be  applied  to  all  those  dry  or  non-bitu- 
minous coals  which,  possessing  from  three  to 
seven  per  cent,  of  a  gaseous  matter,  do  not  swell 
when  burned.  Its  flame  is  quite  short  and 

*Kent's  Steam  Boiler  Economy,  page  42. 


of  a  yellowish  blue  tinge  and  it  can  be  burned 
with  practically  no  smoke.  True  or  dry 
anthracite  is  characterized  by  few  joints  and 
clefts,  and  their  squareness;  great  relative 
hardness  and  density;  high  specific  gravity, 
ranging  from  1.4  to  1.8:  and  semi-metallic 
luster. 

Anthracite  is  now  classed  and  marketed 
according  to  sizes,  the  following  division  of 
mesh  being  adopted  as  standard  at  Wilkes- 
barre  in  1891: 

Egg  Coal  must  pass  through  2}"  mesh  and  not  through  2" 
Stove     "       "       "  "         2"       "         "       "  "       ii" 

Chestnut        "       "  "         ii"     "         "       "  "       \" 

Pea  Coal        "       "  "         1"       "         "       "  "       i" 

Buckwheat  No.  i  must  pass  through  \"  mesh  and  not  through  \" 
Buckwheat  No.  2  or  rice,  must  pass  throug'.i  J"  mesh  and  not 
through  i". 

Semi=anthracite  coal,  because  of  its  con- 
tent of  seven  to  twelve  per  cent,  of  volatile 
combustible,  kindles  more  readily  and  burns 
more  rapidly  than  anthracite.  It  has  less 
density,  hardness,  and  metallic  luster  than 
anthracite  and  the  usual  specific  gravity  is 
about  i  .40. 

Semi=bituminous  coal  is  softer,  contains 
more  volatile  matter,  kindles  easier  and  burns 
more  rapidly  than  anthracite.  It  gives  an 
intense  and  free  burning  fire. 

Bituminous  coals  range  in  color  from  pitch 
black  to  a  dark  brown.  Their  luster  is 
resinous  or  vitreous  in  the  most  compact 
specimens,  and  silky  in  those  showing  traces 
of  vegetable  fibre.  The  specific  gravity  is 
usually  about  1.3.  The  distinctive  charac- 
teristic of  the  bituminous  coals  is  the  emission 
of  yellow  flame  and  smoke  when  burning. 

Bituminous  coals  absorb  moisture  from  the 
atmosphere.  The  surface  moisture  can  be  re- 
moved by  ordinary  drying,  but  a  large  portion 
of  the  water  can  be  separated  from  the  coal 
only  by  heating  it  to  a  temperature  of  about 
250°  F. 

Bituminous  coals  are  either  caking  or  non- 
caking.  The  former  when  heated  fuse  to- 
gether and  swell  in  size;  the  latter  burn 
freely,  do  not  fuse  and  are  commonly  known 
as  "free  burning''  coals.  Caking  coals  are 
usually  rich  in  volatile  hydrocarbons  and  are 
valuable  for  gas  manufacture. 


112 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


Can n el  Coal  is  a  variety  of  bituminous 
coal,  rich  in  hydrogen  and  hydrocarbon,  and  is 
exceedingly  valuable  as  a  gas  coal ;  it  is  bright 
flaming,  burns  without  melting,  and  has  a 
dull  resinous  luster.  It  is  seldom  used  for 
steaming  purposes,  although  it  is  sometimes 
mixed  with  Pocahontas  coal  when  increased 
economy  is  desired  at  very  high  combustion 
rates.  Cannel  coal  usually  shows  the  follow- 
ing composition: 

Fixed  carbon 26  to  55% 

Volatile  Matter 42  to  64 

Earthy  Matter 2  to  14 

The  specific  gravity  is  about  1.24. 

Lignite  is  vegetable  matter  in  the  earlier 
stages  of  conversion  into  coal.  Its  specific 
gravity  is  low,  1.2  to  1.23,  and  when  freshly 
mined  it  contains  as  high  as  fifty  per  cent,  of 


nite  cause  large  stack  losses,  and  in  conse- 
quence it  is  a  low  grade  fuel. 

Composition  of  Coal — The  uncombined 
carbon  in  coal  is  known  as  fixed  carbon. 
There  is  also  some  carbon  combined  with 
hydrogen,  and  this,  together  with  other 
gaseous  substances  driven  off  by  the  applica- 
tion of  heat,  constitutes  the  volatile  portion 
of  the  fuel.  The  fixed  carbon  and  the  volatile 
matter  constitute  the  combustible,*  the 
other  important  ingredients  entering  into  the 
composition  of  coal  being  moisture,  and  the 
refractory  earths  which  form  the  ash. 

A  large  percentage  of  ash  is  undesirable, 
because  it  not  only  reduces  the  calorific  value 
of  the  fuel,  but  in  the  furnace  clogs  up  the  air 
passages  and  prevents  the  rapid  combustion 
necessary  to  high  efficiency.  If  the  coal  also 


TABLE  32 

APPROXIMATE  HEATING  VALUE  OF  GENERAL  GRADES  OF  COAL  PER  POUND 

OF  COMBUSTIBLE,  B.  T.  U. 


PER  CENT.   OF 

COMBUSTIBLE. 

HEATING  VALUE  PER 

KIND  OF  COAL. 

FIXED  CARBON. 

VOLATILE   MATTER. 

POUND  OF  COM- 
BUSTIBLE. 

Anthracite      
Semi-anthracite  .... 

97.0  to  92.5 

02     S   tO  87     C 

3  .  o  to    7.5 

7     <!  to  I  2     < 

14,600  to  14,800 
14  700  to  ic  500 

Semi-bituminous        .... 
Bituminous,  Eastern 
Bituminous,  Western 
Lignite      

87.5  to  75. 
75  .     to  60. 
65.     to  50. 
Under    50 

12.5  to  25. 
25  .     to  40. 
35-     to  50. 
Over       50 

15,500  to  16,000 
14,800  to  15,200 
13,500  to  14,800 
11,000  to  13,500 

moisture.  Its  appearance  is  not  uniform,  and 
varies  from  a  light  brown  color  of  distinctly 
woody  structure  to  specimens  resembling 
hard  coal.  It  is  easily  broken,  will  not  stand 
much  handling  in  transportation,  rapidly 
absorbs  moisture  and  if  exposed  to  the 
weather  it  splits  up  into  fine  pieces  like  air 
slacked  lime,  which  greatly  increases  the 
difficulty  of  burning  it.  It  is  non-caking 
and  gives  a  bright  but  slightly  smoky  flame 
with  moderate  heat. 

Its  composition  is  extremely  variable,  even 
in  the  same  deposit;  the  ash  may  run  as  low 
as  one  per  cent,  and  as  high  as  fifty-eight  per 
cent.  The  high  content  of  moisture  and 
large  amount  of  air  necessary  for  burning  lig- 


contains  an  excessive  quantity  of  sulphur, 
trouble  will  be  experienced  because  sulphur 
is  not  only  injurious  to  boiler  steel,  but  unites 
with  the  ash  to  form  a  fusible  slag  or  clinker 
which  chokes  up  the  grate  bars  and  forms  a 
solid  mass,  having  imbedded  in  it  large 
quantities  of  unconsumed  carbon.  Moisture 
in  coal  is  more  detrimental  than  ash  in  lower- 
ing furnace  temperatures,  because  it  is  not 
only  non-combustible,  but  it  absorbs  heat 
when  it  evaporates  and  is  superheated  to 
the  temperature  of  the  stack  gases. 

Coal  Tables  — The  properties  of  the 
various  classes  of  coals  in  the  progression 
from  lignite  to  anthracite  are  shown  in  Table 
32 .  Data  pertaining  to  the  composition  and 


*The  oxygen  and  nitrogen  contained  in  the  volatile  matter  are  not  really  combustible,  but  through 
custom  the  term  combustible  is  generally  applied  to  that  part  of  the  coal  which  is  dry  and  free  from 
ash,  which  includes  the  oxygen  and  nitrogen. 


UTILIZATION   OF    COAL   DUST 


113 


calorific  value  of  the  principal  coals  in  the 
United  States  are  presented  in  Table  33. 
Preparation  of  this  table  has  been  difficult 
because  of  the  dearth  of  reliable  calorimeter 
tests  on  fuels  from  all  the  various  localities. 
Published  results  are  often  unreliable  be- 
cause of  failure  to  specify  whether  these 
results  apply  to  dry  coal,  or  coal  in  its  natural 
state,  and  also  because  of  doubt  as  to  the 
degree  of  accuracy  of  the  calorimeter  used. 
In  many  cases  it  has  been  necessary  to  com- 
pute the  calorific  value,  but  the  results  thus 
obtained  are  probably  as  nearly  accurate  as 
most  of  the  others  given,  because  of  the 
variation  in  quality  of  samples,  and  dis- 
cordant results  given  by  different  calori- 
meters for  samples  taken  from  the  same  seam 
of  coal.  The  tabular  values  are  therefore  to 
be  regarded  as  approximations  only,  and  in 
any  important  case  a  properly  selected  sample 
of  the  coal  under  consideration  should 
be  submitted  to  a  competent  chemist  for 
determination  of  the  calorific  value. 

Attention  is  called  to  the  difference  between 
the  calorific  value  of  coal  per  pound  of  com- 
bustible and  per  pound  of  fuel.  If  a  coal 
contains  ninety  per  cent,  of  combustible, 
and  has  a  thermal  value  of  14,500  B.  T.  U. 
per  pound  of  combustible,  the  heating  value 
per  pound  of  coal  will  be 

14,500  x  0.90  =  13,050  B.  T.  U. 

In  Table  33  only  the  calorific  values  per 
pound  of  combustible  are  given,  and  the 
value  per  pound  of  coal  containing  any  given 
per  cent,  of  ash  and  moisture  can  be  quickly 
computed  as  above  shown. 

Weathering  of  Coal  produces  results 
which  vary  with  the  kind  of  coal.  Anthracite 
is  but  little  affected,  apart  from  the  oxida- 
tion of  the  sulphur  content,  which  is  small. 
Since  bituminous  coals  usually  contain  a 
higher  percentage  of  sulphur  than  occurs  in 
the  anthracite,  weathering  will  produce  more 
rapid  oxidation,  which  frequently  gener- 
ates sufficient  heat  to  cause  spontaneous 
combustion.  When  this  occurs  the  un- 
affected coal  should  at  once  be  removed, 
and  the  heated  coal  be  spread  so  that  there 
may  be  a  free  circulation  through  it.  When 
it  is  necessary  to  pile  coal  containing  much 
sulphur,  or  expose  it  to  the  weather,  the  risk 
of  spontaneous  combustion  may  be  dimin- 
ished by  making  the  pile  as  shallow  as  pos- 


sible, and  by  inserting  into  it,  at  intervals 
of  six  to  seven  feet,  pieces  of  pipe  which 
stand  vertically,  and  are  open  top  and 
bottom,  so  as  to  promote  the  free  circulation 
of  air  through  the  mass. 

Weathering  destroys  the  coking  property 
of  coals;  it  also  rapidly  disintegrates  some 
lignites  and  renders  them  difficult  to  burn  on 
an  ordinary  grate. 

Sufficiently  complete  experiments  to  de- 
termine the  relation  between  weathering  of 
coal  and  the  decrease  in  its  heat  value  have 
not  yet  been  made.  The  experiments  thus 
far  available  indicate  that  there  is  some  loss; 
probably  the  loss  will  be  greater  as  the  per 
cent,  of  volatile  matter  in  the  coal  is  in- 
creased. Besides  this,  the  augmented  dif- 
ficulty of  burning  weathered  coals  of  low 
grade  must  be  considered. 

It  is  bad  practise  to  pile  coal  on  the  bare 
ground.  When  shoveled  up,  such  coal  will 
invariably  be  mixed  with  more  or  less  dirt, 
gravel,  etc.,  all  of  which  promotes  the  forma- 
tion of  clinkers  and  destruction  of  grates. 

Coal  Dust — The  utilization  of  dust,  slack, 
and  small  sizes  of  coal  that  would  otherwise  go 
to  waste  has  been  the  subject  of  considerable 
investigation  and  experimentation,  resulting 
in  numerous  processes  for  briquetting  the 
material  and  burning  it  in  the  form  of  lump, 
as  before  described;  another  method  which 
has  come  into  favor  in  some  localities  is 
to  pulverize  the  coal  into  a  dust  and  use 
it  as  a  fuel  in  this  form.  From  data  at 
present  available  it  seems  that  advantages 
may  be  expected  from  such  a  fuel,  since 
the  utilization  of  the  combustible  portion 
is  more  complete  than  with  solid  fuel,  the 
production  of  smoke  is  minimized,  and  the 
process  admits  of  an  adjustment  of  the  air 
supply  to  a  point  very  close  to  the  theoretical 
quantity.  This  is  due  to  the  intimate  ad- 
mixture of  the  air  and  fuel,  and  to  the  pos- 
sibility of  maintaining  a  more  nearly  uni- 
form furnace  temperature.  The  principal 
objections  to  the  use  of  coal  dust  as  a  fuel 
are  the  liability  of  the  feed  pipes  and  pas- 
sages adjacent  to  the  furnace  to  choke  up, 
the  difficulty  of  reducing  the  fuel  to  a  uniform 
degree  of  fineness,  liability  of  explosions 
in  the  furnace,  and  the  gathering  of  dust 
on  the  boiler  heating  surface,  thereby  di- 
minishing its  capacity  and  efficiency. 


114 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


TABLE  33 

APPROXIMATE    COMPOSITION    AND    CALORIFIC    VALUE    OF    PRINCIPAL 

AMERICAN  COALS 


LOCALITY   WHERE   MINED. 

PROXIMATE   ANALYSES. 

Approx- 
imate 
Calorific 
Value  in 
B.  T.  U. 
per  Ih. 
of  Com- 
bustible* 

Author- 
ity. 

Volatile 
Matter. 
Per  Cent. 

Fixed 
Carbon. 
Per  Cent. 

Moisture. 
Per  Cent. 

Ash.       Sulphur. 
Per  Cent.  Per  Cent. 

1 

PENNSYLVANIA    ANTHRACITES. 

East  middle  field,  Wharton  bed    . 

3.08 

86.40 

3-71 

6.22 

0.58 

I5,OOO 

(a)  (b) 

"     Mammoth  bed.      ".  .    , 

3.08 

86.38 

4.12 

5-92 

0.49 

I5,OOO 

"     " 

West  middle  field,  Buck  mountain  bed  . 

3-95 

82.66 

3-04 

9.88 

0.46 

1  5,°70 

ii     « 

Seven  foot  bed      ,      . 

3-Q8 

80.87 

3-41 

11.23 

o-S1 

15,080 

"     " 

Primrose  bed 

3-72 

81.59 

5-54 

10.65 

0.50 

15,060 

"     " 

Mammoth  bed 

3-72 

81.14 

3.16 

11.08 

0.90 

15,060 

"     " 

Northern  field,  Mammoth  bed       ... 

4-38 

83.27 

3-42 

8.20 

°-73 

15,100 

"     " 

Southern  field,   Mammoth  bed 

4.28 

83.8l 

3-°9 

8.18 

0.64 

15,100 

"     " 

Primrose  bed 

4-i3 

87.98 

3.01 

4.38 

0.50 

I5.°7° 

"     " 

Lykens  Valley  buckwheat       .      .      . 

6.21 

76.QA 

I  <.3OO 

"  (c) 

6.8 

/  v  y  *r 

80.2 

J  >O 

15,400 

\^  / 

a             n             1  1 

5-° 

81.0 

15.300 

"     " 

PENNSYLVANIA    SEMI-ANTHRACITE. 

Loyalsock     , 

8.10 

83-34 

1.30 

6.23 

1.03 

15,400 

(a)  (b) 

Bernice  basin     

3-56 

82.52 

0.96 

3-27 

0.24 

r5.oso 

"     " 

*  '                        *( 

8.56 

89-39 

1.97 

9-34 

1.04 

r5.475 

"     " 

SEMI-BITUMINOUS. 

Bradford  County     Penna. 

16.95 

69.26 

0.82 

12.29 

0.67 

15,800 

(a)  (d) 

Sullivan  County       

I3-°3 

72.74 

3-24 

10.38 

0.61 

15,70° 

"     " 

Tioga  County     " 

20.50 

67.79 

1.65 

8.85 

1.26 

iS>7S° 

"     " 

Lycoming  County   

I/-53 

72.42 

i.  06 

8.15 

0.84 

15,800 

<i     11 

Center  County   " 

22.60 

68.71 

0.60 

5-40 

2.69 

iS.?00 

"     " 

Huntington  County      .      .      .      ... 

13-84 

78.46 

0.79 

6.00 

0.91 

15,70° 

"     " 

Blair  County      " 

27.27 

60.69 

i.  06 

8.66 

2.31 

iS.SS0 

"     " 

Cambria  County,  lower  bed    . 

21.21 

68.94 

0.74 

7-51 

1.98 

15,75° 

"     " 

upper  bed   .      .      .      " 

17.18 

73-42 

1.14 

6.58 

1.41 

15,800 

"     " 

Clearfield  County,  upper  bed   ..." 

23-94 

69.28 

0.70 

4.62 

1.42 

15,700 

11     n 

lower  bed   .      .      .     " 

21.  IO 

74.08 

0.81 

3-36 

0.42 

15,800 

11     11 

Somerset  County     " 

19.77 

67.78 

I-IS 

9.67 

1.61 

15,800 

"     " 

Broad  Top          " 

17-38 

76.14 

0.78 

4.81 

0.88 

15,800 

i      11 

Cumberland       Md. 

I9-I3 

72.70 

o-95 

6.40 

0.78 

15,820 

"    (e) 

11                                                            ii 

15-47 

73-51 

1.23 

9.09 

0.70 

15,820 

11     11 

"                                                            " 

JS-S2 

74-28 

0.89 

9.29 

0.71 

15,800 

ii     ii 

Pittsburg  seam,  George's  Creek  Valley 

19.19 

74.91 

o-59 

5-31 

0.63 

15,840 

"  (0 

Bakerstown, 

17.17 

72-93 

0.60 

8.76 

0-59 

1:5,840 

II       11 

Upper  Freeport,       " 

17.07 

77.04 

1.02 

4.87 

0.83 

15,800 

II       II 

Lower  Kittanning,  " 

16.92 

76.58 

0.74 

5.86 

0.68 

15,840 

•1       11 

Pocahontas  run  of  mine     ....      Va. 

18.30 

73.65 

0.80 

7-25 

o-57 

!5.78o 

(g) 

"              '  '     *  '       "                                  '  ' 

18.62 

75-12 

0.63 

5-63 

o-57 

15.720 

' 

18.60 

75-75 

0.85 

4.80 

0.62 

15,800 

*Or  coal  dry  and  free  from  ash. 


AMERICAN   COALS 


115 


TABLE   33 — Continued 


LOCALITY   WHERE   MINED. 

PROXIMATE   ANALYSED. 

Approx- 
imate 
Calorific 
Value  in 
B.  T.  U. 
per  lb. 
of  Com- 
bustible. 

Author- 
ity. 

Volatile. 
Matter. 
Per  Cent. 

Fixed 
Carbon. 
Per  Cent. 

Moisture. 
Per  Cent. 

Ash. 
Per  Cent. 

Sulphur. 
Per  Cent. 

New  River  district         ....      W.  Va. 

Quinnamont  lump    

18.65 

79.26 

0.76 

I.I  I 

0.23 

15,820 

(a)  (h) 

slack    

17-57 

79.40 

0.83 

1.92 

0.28 

15.830 

"     " 

Fire  Creek       

22.J4 

75-02 

0.61 

1.47 

0-56 

15,800 

"     " 

Longdale         

21.38 

72.32 

1.03 

5.27 

0.27 

15,800 

"     " 

Nuttalburg     

25-35 

70.67 

i-35 

2.10 

0-57 

15.720 

"     " 

Hawk's  Nest        

21.83 

75-37 

i-93 

1.87 

O.26 

15,800 

"     " 

Ansted      

32.6l 

63.10 

1.40 

2-15 

0.74 

!5.35o 

"     " 

BITUMINOUS. 

Jefferson  County     Penna. 

32-53 

60.99 

I.  21 

3-76 

1.  00 

15.30° 

(i) 

Indiana  County       

29.26 

58.74 

0.98 

9.46 

i-73 

15.400 

<( 

Westmoreland  County 

32.27 

59-23 

I.I4 

5-97 

i-5° 

15,200 

<  t 

Fayette  County       

29-75 

60.47 

o-95 

7.04 

1.79 

15,400 

" 

Potter  County  

32.28 

55-32 

1.72 

9.67 

I.OI 

15,100 

14 

McKean  County      

34-49 

46.25 

2.25 

14.02 

2-97 

14,600 

" 

Clarion  County        

38.60 

54.I5 

1.97 

4.10 

1.19 

14,700 

" 

Armstrong  County  

42-55 

49.69 

1.18 

4-58 

2.OO 

14,000 

" 

Butler  County  

39.88 

48.97 

1.91 

7.22 

1.97 

14,200 

" 

Lawrence  County    

40-45 

52-51 

2.  II 

3-25 

i-37 

14,  5°° 

" 

Beaver  County        

39-04 

50.20 

1.96 

6.96 

2.OO 

14,50° 

" 

Washington  County     .... 

37-n 

5°-99 

1.16 

8.72 

2.06 

14,700 

" 

Greene  County         

35-74 

SI-7S 

1.14 

9.10 

1-79 

14,800 

11 

Youghiogheny  River    

36.49 

59-05 

1.03 

2.61 

1.81 

15,100 

" 

Connellsville      

30.10 

59.61 

1.26 

8.23 

0.78 

15.400 

" 

Upper  Freeport  seam  .      .      .    Pa.  and  O. 

37-35 

5x-63 

i-93 

9.10 

2.89 

14,75° 

(g) 

Jackson  County       Ohio. 

35-79 

52-78 

8.!7 

3-25 

M3 

14,140 

Middle  Kittanning,  Hocking  Valley    .      " 

32-85 

48.74 

6.51 

8-93 

1-58 

14,080 

" 

MahoningCoal,  Salinville                            " 

35-oo 

5°-95 

3.i5 

10.90 

1.86 

i4,73o 

<  ( 

Massillon       " 

31-83 

64-25 

2-47 

i-45 

0.56 

15-075 

(a) 

Brier  Hill     " 

34.60 

56-30 

4.80 

4-3° 

14,300 

(k) 

Big  Stone  Gap  splint     .      .      .        Virginia. 

33-90 

59-25 

i.  80 

5-°5 

0.71 

15,100 

(a)  (c) 

Carbon  Hill        

18.60 

71.00 

0.40 

IO.OO 

15,800 

Coal  River   

35-89 

\J  >J          s 

58.89 

3-35 

I-25 

0.62 

14,95° 

"     " 

Coal  River  splint     

33-33 

55-25 

1.78 

9.02 

0.62 

15,000 

"     " 

Cedar  Grove,  Kanawha  Co. 

34.08 

60.67 

2.10 

2.50 

0.65 

15.^0 

'     " 

Richmond  coking  coal         ...        " 

30-36 

58-30 

1.62 

10.58 

*5.35o 

"     " 

South  of  James  River   .... 

32.24 

58.89 

1.48 

7.72 

i-45 

15,200 

"     " 

Thacker        W.  Va. 

35-54 

56-24 

I.38 

6.84 

i-39 

iS.^o 

(g) 

Coal  Creek,  Anderson  County        .      .Tenn. 

34-86 

58.41 

1.29 

5-44 

O.2O 

*S,°5° 

(a)  (c) 

Etna,  Marion  County    " 

23-72 

63-94 

0-94 

11.40 

I.I9 

15,70° 

«     a 

Franklin  County     .      .      .      .  '   .      .      " 

25-41 

62.00 

1.77 

10.82 

0.64 

*5>75° 

"     " 

Harriman     " 

32-32 

62.31 

5-37 

0.84 

JS^S0 

1  1     <  i 

Melville,  Hamilton  Co  " 

26.50 

67.08 

2.74 

3-68 

0.98 

^^S0 

«     « 

Morgan  County  

34-55 

61.66 

!.67 

2.14 

0.88 

*5^5° 

(i     « 

116 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


TABLE  33— Continued 


PROXIMATE   ANALYSES 

Approx- 
imate 

Calorific 

LOCALITY   WHERE   MINED. 

Volatile 
Matter. 
Per  Cent. 

Fixed 
Carbon. 
Per  Cent 

Moisture. 
Per  Cent. 

Ash. 
Per  Cent. 

[Sulphur. 
Per  Cent. 

Value  in 
B.  T.  U. 
per   Ib. 
of  Com- 

Author- 
ity. 

bustible. 

Newcombe,  Campbell  Co.  .      .      .        Tenn. 

33-77 

60.64 

3-59 

1  .20 

15,200 

(a)  (c) 

Rhea  County      

29.13 

61.68 

0.82 

7.07 

1.30 

1SA5° 

«     « 

Rock  wood,  Roane  Co.         .... 

26.62 

60.  II 

r-75 

11.52 

1.49 

15.050 

"     " 

Scott  County      " 

34-53 

61.66 

1.67 

2.14 

0.88 

I5,2OO 

"     " 

Tracy  City,  Suanee  Co  

29.30 

61.00 

i.  60 

7.80 

r5,45° 

"     " 

Boyd  County            ....     Kentucky. 

33-77 

54-51 

3-27 

8.91 

I.56 

14,95° 

(a)    (1) 

Carter  County   

34.60 

55^5 

4.10 

4-77 

I-4I 

14,850 

"     " 

Coalton  County        .... 

32.04 

55-59 

5-J9 

6.71 

1.68 

15,100 

"     " 

Floyd  County    

36.70 

5J-7o 

1.30 

10.30 

1.36 

14,400 

"     " 

Greenup  County      .... 

35-00 

52-34 

3-56 

9.02 

2-59 

14,600 

"     " 

Johnson  County       .... 

38.04 

56-30 

2.66 

3-oo 

1.29 

14,600 

"     " 

Lawrence   County  .... 

35-70 

53-28 

4.60 

6.42 

i.  08 

14,600 

"     " 

Martin  County  

32.60 

62.68 

1.46 

3-26 

15.30° 

"     " 

Pike    County      

26.80 

67.60 

i.  80 

3.80 

o-97 

15,600 

"     " 

Bibb  Co.,  Blockton,  upper  vein      .      .     Ala 

34-oi 

59-51 

2.28 

3-25 

0-45 

1S^5° 

(c) 

Cahaba,  Shelby  County      .... 

33-28 

63.04 

1.66 

2.02 

0-53 

15,400 

(m) 

Conglomerate    " 

30.86 

64-54 

2.13 

2-47 

1.48 

15.45° 

" 

Helena    " 

29.44 

66.  81 

1.  21 

2-54 

0-53 

^.OS0 

<  < 

Pratt  Co.'s  Upper  Jefferson  Co. 

32.29 

59-50 

1.47 

6.73 

1.22 

i5.250 

" 

Pratt  Co.  's,  Lower  Jefferson  Co.    . 

30.68 

63.69 

i-S3 

4.10 

0.6l 

*5»45° 

11 

Brazil      Indiana. 

34-49 

50-30 

8.98 

6.28 

!-39 

i4,55o 

(a) 

Block  Coal    

38-17 

52.27 

4.66 

5-89 

13,880 

(n) 

Big  Muddy   Illinois. 

3i-9 

53-o 

7-7 

7-4 

14,55° 

(o) 

Carterville  mine  run 

34-n 

52-17 

4-87 

8.85 

0.85 

14,150 

(P) 

washed,   No.  i 

33-99 

54-21 

4.66 

7.14 

0.74 

!3,93° 

'  ' 

No.  2. 

35-12 

55-or 

4-3i 

5-56 

0.86 

14,35° 

" 

No.  4. 

33-26 

55-29 

4.86 

6-59 

I-I5 

i3,94o 

" 

Collinsville,  Madison  Co.     . 

45-89 

3i-57 

9.20 

J3-34 

5-34 

13,080 

1  ' 

Danville,  Vermilion  Co  

43-7° 

45-37 

4-78 

6-15 

14,  050 

" 

screenings 

33-So 

34.20 

9.40 

23.10 

13,760 

1  * 

Duquoin,  Perry  Co.,  lump 

34.61 

50-85 

9.14 

5-40 

14,110 

'  ' 

nut 

38.91 

46.00 

7-43 

7.66 

L3,098 

4  * 

slack 

35-95 

41.60 

6.05 

16.40 

S-M 

14,37° 

" 

Glen  Carbon,  Madison  Co.,   lump. 

39-T3 

40.66 

7-85 

12.36 

4.87 

14,466 

'  ' 

Girard,  Macoupin  Co  

34-39 

45-76 

9.70 

10.15 

3-5° 

1  2,410 

'  * 

La  Salle  

39-40 

43-95 

8.22 

8-43 

14,600 

Mt.  Olive      

38.33 

40.22 

9-63 

11.82 

6.78 

14,090 

(o) 

Mt.  Olive      

33-i 

44.1 

8.1 

14.7 

13,70° 

4  * 

Pana,  Christian  Co.,  nut 

39-43 

46.04 

5-30 

9-23 

13,860 

(P) 

Pana,  Christian  Co.,  slack  . 

35-45 

39-35 

8-55 

16.65 

4-77 

13,100 

*  4 

St.  John,  paradise  lump 

37.00 

51.10 

9-63 

2.27 

13,590 

*  * 

Stanton,  Macoupin  Co.,  lump 

36.00 

48.00 

Dried 

16.00 

13.70° 

*  * 

Streator,  average    

37-63 

45-93 

8.30 

8.14 

13,730 

4  ( 

lump        

39-40 

48.20 

Dried 

12.40 

14,400 

AMERICAN   COALS 


117 


TABLE  33— Continued 


LOCALITY   WHERE   MINED. 

PROXIMATE   ANALYSES. 

Approx- 
imate 
Calorific 
Value  in 
B.  T.  U 
per  lb. 
of  Com- 
bustible 

Author- 
ity. 

Volatile 
Matter 
Per  Cent 

I  ixed 
Carbon 
Per  Cent 

Moisture 
Per  Cent 

Ash. 
Per  Cent. 

Sulphui 
Per  Cent 

Streator  nut       Illinois 

35-6° 

54-5° 

Dried 

9.90 

I4,2OO 

(P) 

screenings       .... 

38.40 

43.80 

Dried 

17.80 

14,100 

" 

Trenton  Clinton  Co  

30.4.0 

S2.OO 

1  3.^0 

4.  3O 

O.QO 

12,850 

" 

Vulcan,  St.  Clair  Co.,  nut   . 

o     ^ 

30.86 

o 

45-°9 

O    O 

7-44 

*f*O 

16.61 

*  y 
1.30 

12,440 

it 

Cleveland,  Lucas  Co  Iowa 

39-76 

42.12 

6.66 

11.48 

I  1,  660 

(q) 

Cincinnati  Co  

26.58 

40-03 

23-99 

9-i3 

14,850 

*  ' 

Hiteman,  Tyrone  Co  

37-6^ 

44.69 

4.92 

12.76 

1  1  ,480 

" 

Steam  coal,  Beacon  Co. 

O  I         O 

35-64 

"T-  .    ^    -y 

38.09 

"      ,7 

4.09 

/ 

20.37 

12,830 

» 

Walnut  block,  Centerville 

37-77 

46.64 

5-52 

10.07 

12,460 

ii 

Smoky  Hollow,  Avery  Co. 

39.02 

5J-33 

6.29 

4-35 

II,37° 

" 

Whitebreast  Fuel  Co.,  Pekay  . 

46.06 

46.89 

£^ 

7-05 

2.8? 

14,020 

(y) 

Eldon  Coal  Co.,  Laddsdale 

42.72 

47.78 

3    ro 
w  °^ 

9-5° 

4.96 

i4,520 

" 

Mine  No.  2,  Hocking     .... 

45.18 

45-34 

•  ts\ 
'3    "*00 

9.48 

3-98 

13,870 

" 

Des  Moines  Coal  Co.,  Marquisville 

45.62 

50.29 

^  G  ° 

o  °o 

4-09 

2-74 

12,560 

" 

Lunsden  Coal  Co.,  Bloomfield 

39.66 

53.46 

.<£  <% 

T3_   5 

7.48 

2.38 

13,920 

" 

Whitebreast  Fuel  Co.,  Hilton  . 

40.61 

48.21 

.215  * 

±!'C  ^ 

ii.  18 

3-26 

13,95° 

" 

Block  Coal  Co.,  Centerville       .      . 

37-79 

54.85 

>^  «J  8f 

c  >  £ 

7-36 

3-29 

13,690 

11 

Consolidation  Coal  Co.,  No.  10,  Buxton  " 

37-09 

50-83 

£-  « 

>  cs  > 

12.08 

2.27 

13,690 

" 

Crowe  Coal  Co.,  Boone 

41.46 

50-33 

IS* 

8.21 

4.16 

13,860 

" 

Corey  Coal  Co.,  Lehigh 

37-98 

47.98 

""•a*. 

^  G  f- 

14.04 

5-90 

14,460 

" 

D.  Lodwick,  Mystic 

39-07 

54-91 

uS* 

6.02 

3-15 

13,690 

" 

Platt  Coal  Co.,  Van  Meter        .      . 

40-54 

51.04 

eSi     l 
0   M 

8.42 

3.68 

i3,39o 

" 

Jasper  Co.  Coal  Co.,  Colfax 

42.24 

50.27 

co.SS 

7-49 

3-08 

13,  II0 

" 

Pittsburg      Kansas. 

28.60 

60.32 

3.26 

7.28 

11,030 

(q) 

Weir  City,  No.  i       

33-54 

58.41 

2.08 

5-97 

12,35° 

" 

Weir  City,  No.  5       

33-77 

57-17 

2.70 

6.36 

12,850 

" 

Central  C.  &  C.  Co.,  No.  66,  Macon  Co.     Mo. 

39.10 

41.83 

12.  OO 

7-07 

3-44 

12^,580 

a)  (r) 

Central  C.  &  C.  Co.,  No.  70,  Macon  Co. 

36.26 

43.16 

10.20 

10.38 

4-47 

^.iS0 

Elliott  Coal  Co..  Randolph  Co.       .      . 

36-32 

42.77 

11.15 

9.76 

3-55 

13,120 

11     (i 

Far.  Consolidated,  No.  6,  Lafayette,  Co.    " 

36.14 

44.70 

n-95 

7.21 

2-57 

12,890 

<i     11 

Marceline  Coal  Co.,  Linn  Co.    ...        " 

33-25 

47.27 

9-45 

10.03 

5-73 

13,420 

11     ii 

Mendota  Coal  Co.,  No.  2,  Putnam  Co. 

34-n 

39-85 

J7-59 

8-45 

3.21 

1,840 

11     11 

Murline  Coal  Co.,  Ray  Co. 

37-35 

41.66 

I3-°7 

7.42 

1.92 

2,660 

ii     11 

Richmond  &  Camden  Coal  Co.,  Ray  Co.     " 

37-93 

42.99 

9-83 

9-25 

3-n 

2,620 

11     11 

Weir  Coal  Co.,  No.  3,  Barton  Co.   . 

34-40 

53-98 

3.62 

8.00 

4.02 

5,000 

it     ii 

Western  Coal  Co.,  No.  8,  Barton  Co.   . 

35-73 

53-72 

2-35 

8.20 

4.10 

5,020 

11     K 

Hezron  lump      Colorado. 

37-52 

54-39 

Jried 

8.09 

2,970 

(8) 

Walsen  run  of  mine 

36.02 

51.12 

Dried 

12.86 

2,130 

Bridgeport  Coal  Co.,  Wise  Co.        .      Texas. 

31-93 

41.12 

12.21 

14.74 

J-73 

4,47° 

(t) 

Cannel  Coal  Co  .  ,  Webb  Co  .       .      . 

48.84 

36.61 

3-46 

11.09 

2.09 

4,080 

Cisco,  Eastland  Co  " 

34-86 

36.37 

13-44 

I5-33 

2-54 

3,47° 

" 

Eagle  Pass,  Maverick  Co.    . 

33-oS 

40.09 

9.40 

T7-43 

1.28 

5,23° 

" 

Rio  Grande  Coal  Co.  ,  Webb  Co.     . 

47-95 

38-89 

4.09 

9.07 

2-45 

2,720 

ii 

Strawn,  Palo  Pinto  Co. 

3I-78 

42.04 

4.00 

22.18 

2-39 

5,600 

" 

Texas  &  Pacific  Coal  Co.,  Erath  Co. 

33-2° 

43-!5 

5-83 

17.82 

J-S1 

5,000 

1  1 

118 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


TABLE  33— Continued 


PROXIMATE   ANALYSES. 

Approx- 
imate 

Calorific 

Value  in 

Author- 

LOCALITY   WHERE    MINED. 

Volatile 
Matter. 
Per  Cent. 

Fixed 
Carbon. 
Per  Cent. 

Moisture. 
Per  Cent. 

Ash. 
Per  Cent. 

Sulphur. 
Per  Cent. 

B.  T.  L. 

per   Ib. 
of  Com- 

ity. 

bustible. 

LIGNITES  AND  LIGNITIC  COALS 

Calvert  Bluff  ,  Robertson  Co.    .      .      Texas- 

51.00 

IO.OO 

29.86 

9.14 

0.91 

I3,OOO 

(t) 

Como  Coal  Co.,  Hopkins  Co.     . 

45.88 

3-41 

33.87 

16.84 

0.68 

13,100 

" 

Glenn-  Belto  mine,  Bastrop  Co.     . 

36.88 

21.22 

35-40 

6.50 

0-94 

13,530 

'  * 

Houston  Co.  Coal  Co  

33-16 

J9-93 

36.16 

IO-75 

0.40 

14,140 

'  ' 

Lytle,  Medina  Co  

40.31 

18.50 

34-29 

6.90 

i  .20 

I2,8OO 

'  ' 

North  Texas  Coal  Co.  ,  Wood  Co.   . 

45-21 

II.  60 

35-60 

7-59 

0-47 

13,460 

'  ' 

Rockdale,  Milam  Co  

34.26 

22.73 

34-72 

8.29 

1.04 

13,100 

*  * 

Timson  Coal  Co.,  Shelby  Co.    . 

39-53 

23-05 

31.96 

5-46 

1.46 

12,870 

'  ' 

Cumberland       Wyoming. 

44.27 

46.18 

3-65 

5-9o 

0.61 

I4,IOO 

(u) 

Hanna     

48.43 

36.37 

6.38 

8.82 

o-99 

13,440 

(v) 

Kemmerer    

36.16 

51-78 

5.80 

6.26 

0.60 

13,630 

(u) 

Rock  Springs     

40.83 

48.30 

7.19 

3.68 

0.38 

13,900 

*  4 

Black  Diamond       ....       Colorado. 

43-05 

39.01 

14.67 

3-27 

0.77 

10,507 

(c) 

Erie  

32-7r 

45-98 

18.57 

2-74 

0.52 

11,360 

*  ( 

Canon  City,    vertical    .... 

37-61 

5^36 

7.01 

4-03 

i.  02 

13,097 

*  * 

upper       .... 

36.74 

47-93 

6.56 

8.76 

0.62 

I  I  ,1  70 

'  * 

"       lower  

37-21 

49-54 

7.66 

5-59 

0.82 

11,644 

4  * 

Golden  City,     5  foot  seam       .      .        " 

36.20 

42.08 

18.35 

3-37 

0-43 

8,154 

i  l 

"        12     '                   "... 

41-23 

38.46 

17.64 

2.67 

0.30 

9,947 

11 

Gunnison  River       

12.  16 

84-65 

1-50 

2.29 

0.70 

14,240 

*  * 

Marshall        

37-84 

46.43 

I3.I9 

2-54 

0.66 

11,478 

*  * 

Mount  Carbon  

36.91 

37-82 

20.38 

4.87 

0.40 

10,624 

*  * 

South  Park         

33-79 

58.62 

6.30 

1.28 

0.47 

12,204 

1  i 

Castle  Gate                                 .      .        Utah. 

IT  8 

Si  .3 

6.9 

14,180 

(w) 

Black  Diamond       .      .      .      .Washington. 

43.18 

0       J 

49.81 

4-32 

7 

2.69 

0.76 

13,600 

(x) 

Carbon  Hill  No.  4  Vein 

37.02 

49.12 

I.  O2 

12.84 

14,600 

" 

Occidental,  No.  6,  Renton 

37-40 

52.55 

2.  02 

8.03 

0.68 

14,020 

4  * 

Renton  Cooperative  Co.  No.  2  Vein    " 

37.38 

53-6o 

3-44 

5-58 

o-73 

13,830 

" 

Roslyn  mine,  No.  4  . 

38.20 

49.40 

i  .90 

10.50 

0.41 

14,590 

" 

Roslyn  mine,  Cle-Elum 

37-86 

48.30 

6-34 

7-59 

0.49 

U,730 

" 

Skaget  Coal  &  Coke  Co.       .      . 

26.67 

64.51 

o-53 

8.20 

0.68 

15,530 

" 

Wilkeson,  C.  &  C.  Co.,  No.  i  mine 

28.11 

6i.53 

0.63 

9-73 

2.09 

!5>59o 

REFERENCES:  (a)  B.  T.  U.  computed  by  Table  No.  49  and  Fig.  27.  (b)  Analyses  from  Kent's  Mechan- 
ical Engineer  s  Pocket-Book,  p.  625.  (c)  Selected  analyses.  (d)  Kent's  Steam  Boiler  Economy,  p.  59. 
(e)  Kent's  Pocket-Book,  pp.  625-6.  (f)  Analyses  by  W.  B.  Clark,  (g)  Lord  and  Haas'  researches, 
(h)  Steam  Boiler  Economy,  p.  65.  (i)  Ibid.,  p.  61.  (k)  Steam  Boiler  Economy,  p.  46.  (1)  Ibid.,  p.  65. 
(m)  Ibid.,  p.  67.  (n)  D.  P.  Jones,  (o)  Steam  Boiler  Economy,  p.  73.  (p)  Twentieth  Annual  Coal  Re- 
port, Illinois,  1902.  (q)  C.  R.  Richards,  (r)  Sixteenth  Report  of  Coal  Mine  Inspector,  Missouri,  1902. 
(s)  Colorado  Fuel  and  Iron  Co.  (t)  Bulletin  No.  15,  University  of  Texas.  (u)  Union  Pacific  Coal  Co. 
(v)  Slosson  and  Colburn.  (w)  Carpenter,  (x)  Third  Biennial  Report  of  Bureau  of  Labor,  State  of  Wash- 
ington, 1901-2.  (y)  Notes  on  Steam  Generation  with  Imva  Coal,  by  G.  W.  Bissell,  M.  E.  in  Bulletin  No.  9. 
Engineering  Experiment  Station,  Iowa  State  College. 


CALORIFIC  VALUE   OF   WOOD 


119 


Patent  or  Pressed  Fuels — Among  these 
may  be  classed  fuels  composed  of  the  dust  of 
some  suitable  combustible,  pressed  and  ce- 
mented together  by  a  substance  possessing 
adhesive  and  inflammable  properties.  Such 
fuels,  known  as  briquettes,  are  extensively 
used  in  France,  and  consist  of  carbon  or  soft 
coal,  too  small  for  ordinary  commercial  use, 
mixed  with  pitch  and  coal  tar.  They  do 
not  find  much  favor  in  this  country,  as  the 
cost  and  difficulty  of  manufacture  render 
them  no  more  economical  than  coal. 

Coke  is  produced  in  three  ways:  (i) 
From  gas  coal,  in  gas  retorts;  (2)  From  gas 
or  ordinary  bituminous  coal,  in  special  ovens. 
(3)  From  petroleum,  by  carrying  the  dis- 
tillation of  the  residuum  to  a  red  heat.  The 
process  of  manufacture  necessitates  expelling 
the  hydrocarbon  gases,  hence  coke  is  a  porous 
product  consisting  almost  entirely  of  carbon. 
It  is  a  smokeless  fuel,  it  readily  attracts  and 
retains  water  from  the  atmosphere,  and  if  not" 
kept  under  shelter  it  may  absorb  twenty  per 
cent,  of  its  weight  of  moisture. 

TABLE  34 
ANALYSES  OF  AMERICAN  COKES 

(Kentucky  Geological  Survey') 


WHERE  MADE. 

NO.  OF 

TESTS. 

FIXED 
CARBON. 

ASH. 

SULPHUR. 

Connellsville,  Pa    . 

3 

88.96 

9-74 

0.810 

Chattanooga,  Tenn 

4 

80.51 

16.34 

i  -505 

Birmingham,  Ala. 

4 

87.29 

10.54 

i-  195 

Pocahontas,  Va. 

3 

92.53 

5  •  74 

o.  597 

New  River,  W.  Va. 

8 

92.38 

7.21 

o.  562 

Big  Stone  Gap,  Ky. 

7 

93-23 

5-69 

0-749 

Coke  from  gas  works  is  usually  softer  and 
more  porous  than  other  kinds.  It  ignites 
more  readily  and  burns  with  less  draft  than 
is  required  for  the  combustion  of  coke  pro- 
duced in  ovens.  It  does  not  produce  so 
intense  a  heat,  hence  it  is  not  used  extensively 
in  factories  where  a  smokeless  fuel  with  great 
heat  is  needed.  Oven  coke  is  a  dead  gray 
black  in  color,  porous  and  brittle,  with  a 
slightly  metallic  luster.  It  is  used  principally 
in  blast  furnaces,  cupolas,  smelting  and  other 
furnaces  requiring  a  blast.  Petroleum  coke 
occurs  in  large  irregular  lumps,  is  a  compro- 
mise in  hardness  between  oven  and  gas-retort 
coke, blacker  in  color  than  either  of  the  other 
classes  and  is  used  principally  for  making 
electric  carbons. 


Peat  contains  a  large  amount  of  water, 
averaging  seventy-five  to  eighty  per  cent., 
and  occasionally  reaching  ninety  per  cent. 
It  is  unsuitable  for  fuel  until  dried,  and  its 
composition  then  varies  little  from  that  of 
wood.  The  proportion  in  which  the  various 
primary  constituents  exist  in  dried  peat  is 
about  as  follows: 


Carbon 

Hydrogen 

Oxygen. 

Nitrogen 

Ash 


58  to     60% 
6 

30  to  31 
1.25  to  1.5 
2.75  to  5 


Some  peats  have  been  known  to  show 
eleven  per  cent,  of  ash.  In  computing  the 
heat  of  combustion,  it  must  be  borne  in  mind 
that  peat  as  usually  dried  in  the  air  contains 
from  twenty-five  to  thirty  per  cent,  of  water. 
While  large  deposits  of  peat  are  found  in  this 
country  it  has  not  thus  far  been  found 
profitable  to  utilize  them  in  competition 
with  coal. 

Wood  is  vegetable  fiber  which  has  not 
undergone  geological  changes,  but  usually 
the  term  is  used  to  designate  the  compact 
substances  familiarly  known  as  tree  trunks 
and  limbs.  When  newly  felled,  wood  con- 
tains moisture  ranging  from  thirty  to  fifty  per 
cent,  by  weight,  and  midway  between  these 
figures  is  considered  a  good  average.  After 
a  year's  ordinary  drying  in  the  atmosphere, 
the  moisture  is  reduced  to  about  eighteen  to 
twenty-five  per  cent. 

Wood  is  usually  classified  as  hard  and  soft. 
Hard  woods  include  oak,  maple,  hickory, 
birch,  walnut  and  beech.  Soft  woods  con- 
sist of  pine,  fir,  spruce,  elm,  chestnut,  poplar 
and  willow.  Hard  woods  give  less  heat  per 
pound  than  soft  woods,  contrary  to  general 
opinion.  Gottlieb  's  experiments  proved  that 
a  pound  of  white  pine  has  a  heat  value  8.25 
per  cent,  more  than  that  of  white  oak. 
Weber's  experiments  with  fir  (soft)  and  oak 
(hard)  gave  the  following  results: 

FIR.  OAK. 

Carbon 51-08%     5°  -43% 

Hydrogen    .      .      .      .      .      6.12  5.88 

Oxygen  and  Nitrogen        .42.90         43  . 69 
Calorific  Value,  B.  T.  U.    .     8,790          7,440 

From  Table  36  it  appears  that  about  if 
Ibs.  of  dry  wood  have  the  same  calorific  value 
as  one  pound  of  bituminous  coal;  also  that 


120 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


the  heating  value  of  the  same  weight  of 
various  woods  does  not  vary  over  ten  per 
cent.  The  table  is  based  on  dry  wood,  but 
woods  in  ordinary  air-dried  condition  contain 
about  twenty  to  twenty-five  per  cent,  of 
moisture,  hence  the  available  heat  producing 
content  will  be  twenty  to  twenty-five  per  cent. 

TABLE  35 
RELATIVE  CALORIFIC  VALUE  OF  WOODS 


WOOD. 

SPECIFIC 
GRAVITY. 

LBS.   IN  ONE 
CORD. 

LBS.   COAL 
EQUIVALENT 
TO    ONE    CORD 
OF  WOOD.* 

Hickory,  shell  bark 

I  .OOO 

4469 

1910 

Oak,  chestnut 

0.885 

3955 

1690 

Oak,  white 

0.885 

3821 

1670 

Ash,  white 

0.772 

3450 

1440 

Dogwood    . 

0.8l5 

3643 

1560 

Oak,  black 

0.728 

3254 

1390 

"       red    . 

0.728 

3254 

1  3  90 

Beech,  white 

0.724 

3236 

1380 

Maple,  hard  (sugar) 

0.644 

2878 

1230 

Maple,  soft 

0-597 

2668 

1140 

Cedar,  red 

0.565 

2525 

1080 

Magnolia     . 

o.  605 

2704 

1  1  60 

Pine,  yellow 

0.551 

2463 

1060 

Sycamore  . 

0.535 

2391 

IO2O 

Butternut  . 

0.567 

2534 

1090 

Pine,  New  Jer  ey 

0.478 

2137 

916 

pitch 

0.426 

1904 

812 

"       white 

0.418 

1868 

800 

Poplar,  Lombardy 

0.397 

1774 

761 

Chestnut     . 

0.552 

2333 

I  OOO 

Poplar,  yellow 

0.563 

2516 

1080 

less  than  in  the  table,  and  of  the  heat  pro- 
duced a  part  is  absorbed  in  evaporating  the 
water  in  the  wood  and  superheating  the  steam 
thus  formed.  The  heat  so  absorbed  may  be 
computed  by  formula,  page  133,  and  the  net 
calorific  value  of  the  wood  may  thus  be  deter- 
mined if  the  per  cent,  of  water  is  known.  As 


a  general  average  one  per  cent,  of  water  will 
make  a  reduction  of  one  and  one-half  per  cent, 
in  the  heating  value  of  wood.  Since  a  pound 
of  average  bituminous  coal  is  equal  in  evapo- 
rative power  to  about  one  and  three-fourths 
pounds  of  dry  wood,  or  about  two  and  one- 
third  pounds  of  wood  containing  twenty-five 
per  cent,  of  moisture,  the  value  of  a  cord  of 
wood  expressed  in  pounds  of  coal  may  with 
sufficient  accuracy  for  practical  purposes 
be  taken  from  Table  3  5 . 

Spent  Tan,  which  consists  of  the  fibrous 
portion  of  the  bark,  is  thirty  per  cent,  by 
weight  of  the  original  oak  bark.  The 
calorific  value  of  dry  tan,  containing  fifteen 
per  cent,  of  ash,  is  6,100  B.  T.  U.  per  pound, 
while  tan  in  the  average  state  of  dryness  con- 
tains thirty  per  cent,  of  water  and  has  a 
heating  value  of  4,284  B.  T.  U.  The  con- 
ditions for  burning  tan  and  all  other  similar 
wet  fuels  require  that  they  be  surrounded  with 
heated  surfaces  and  burning  fuel,  in  order  that 
they  may  be  dried  rapidly,  and  thorough 
combustion  be  secured. 

Straw  is  one  of  the  many  inferior  grades 
of  fuel  which  are  sometimes  used  when  other 
fuels  could  be  obtained  only  with  difficulty 
and  at  greater  cost.  Table  37,  on  following 
page,  gives  the  relative  composition  of  wheat 
and  barley  air-dried  straw. 

Such  straws  have  a  calorific  value  of  5411 
B.  T.  U.  per  pound  according  to  Dulong's 
formula,  [24]  and  weigh  when  pressed  six  to 
eight  pounds  per  cubic  foot.  Experiments 


TABLE  36 
COMPOSITION  AND  CALORIFIC  VALUES  OF  VARIOUS  DRY  WOODS   (Gottlieb) 


CALORIFIC 

KIND  OF  WOOD 

CARBON 

HYDROGEN 

NITROGEN 

OXYGEN 

ASH 

VALUE  B.T.U. 

% 

% 

% 

% 

% 

PER  LB. 

Oak       .      .     .      . 

50.16 

6.  02 

0.09 

43-36 

°-37 

8,316 

Ash       .  •-,  .      .      . 

4Q  .  1  8 

6  .  27 

O  .  O7 

A  -2      QI 

O  .  S7 

8,480 

Elm       .... 

t^y 
48.99 

/ 

6.  20 

/ 
O.O6 

T^O       7 
44-25 

J  •  J  1 
0.50 

v  }*f-v  •* 

8,510 

Beech    .... 

49  .06 

6.  ii 

0.09 

44.17 

o-57 

8,591 

Birch    .... 

48.88 

6.06 

O  .  IO 

44.67 

o  .  29 

8,586 

Fir  

t;o  .  36 

<;  .  02 

o.o< 

4.3  .  30 

0.28 

0,063 

Pine      .... 

o       o 

50-31 

o    y 
6  .  20 

J 

0.04 

T^O       O7 

43.08 

o-37 

s  *         O 

9»i53 

Poplar! 

49-37 

6.  21 

0.96 

41  .60 

1.86 

7,834t 

Willow  t     .      .      . 

49.96 

5-96 

0.96 

39-56 

3-37 

7,926! 

*On  basis  i  Ib.  coal  =  2$  Ibs.  wood.      JValues  according  to  Chevandier.      fValues  by  Formula  No.  24. 


CALORIFIC  VALUE  OF  BAGASSE 


121 


in  Russia  show  that  winter  wheat  straw, 
dried  at  230°  F.  gave  a  heating  value  of 
6,290  B.  T.  U.  when  dry  and  5,448  B.  T.  U» 
when  containing  ten  per  cent,  of  moisture. 

Other  straws  gave  a  calorific  value  varying 
from  6,750  B.  T.  U.  per  pound  for  flax  to 
5,590  for  buckwheat. 

TABLE  37 

COMPOSITION    OF   WHEAT  AND  BAR- 
LEY STRAWS 


WHEAT 

BARLEY 

MEAN 

STRAW 

STRAW 

VALUE 

Carbon    . 

•35-86% 

36.27% 

36.00 

Hydrogen 

.     5.01 

5-°7 

5.00 

Oxygen   . 

.37.68 

38.26 

38.00 

Nitrogen  . 

•    o-45 

0.40 

0.50 

Ash      . 

.5.00 

4-5° 

4-75 

Water      .      . 

.16.00 

I5.50 

15-75 

Bagasse,  or  Megass,  is  the  name  given  to 
refuse  sugar  cane  after  the  juice  has  been 
extracted.  It  is  used  largely  on  sugar  planta- 
tions as  a  fuel  for  generating  the  steam 
required  in  operating  the  mills;  upon  the 
efficient  use  of  bagasse  as  a  fuel  depends  to  a 
great  extent  the  success  of  sugar  raising  as  a 
financial  proposition,  particularly  where  the- 
prices  for  sugar  are  low  and  the  cost  of  coal 
delivered  is  high. 

The  heating  value  of  bagasse  depends 
mostly  upon  the  fibrous  matter  of  the  cane. 
This  varies  in  different  countries  but  in 
general  is  greater  as  the  age  of  the  cane  is 
increased.  In  Cuba,  Hawaii,  and  the  West 
Indies,  the  cane  is  left  standing  from  twelve 
months  to  two  years  and  the  fibrous  matter 
will  run  from  eleven  to  twenty  per  cent.  In 
Louisiana,  where  the  frosts  require  the  cane 
to  be  harvested  after  a  life  not  exceeding  six 
and  one-half  months,  the  weight  of  the  fiber 
will  not  be  more  than  nine  or  ten  per  cent. 
The  tropical  canes  therefore  have  a  much 
greater  fuel  value,  and  even  with  inefficient 
machinery  the  mills  can  be  operated  solely 
by  the  bagasse  produced.  It  is  very  seldom 
that  such  results  can  be  obtained  where  the 
fiber  is  less  than  twelve  per  cent,  of  the  weight 
of  the  cane;  consequently  in  the  sugar  mills 
of  the  United  States  supplementary  boilers 
fired  with  coal  are  required.  The  economy 
of  the  mill  is  estimated  by  the  number  of 


pounds  of  coal  or  wood  required  per  ton  of 
sugar  produced. 

The  average  composition  of  Louisiana  cane 
when  ready  to  be  ground  is  ten  per  cent,  fiber 
and  ninety  per  cent,  juice.  The  juice  con- 
sists of 

85   %  Moisture 
10   %  Sugar 
5  %  Molasses, 

which  makes  the  composition  of  sugar  cane 
76.5   %  Moisture 
9.0%  Sugar 
4.5%  Molasses 
10. o  %  Fiber 

In  passing  through  the  mills  the  content  of 
juice  extracted  varies  from  75%  to  82%  of  the 
weight  of  cane,  the  average  extraction  being 
about  78%.  Assuming  100  Ibs.  of  cane,  78 
Ibs.  of  juice  will  be  extracted,  leaving  22  Ibs. 
of  bagasse,  consisting  of  10  Ibs.  of  fiber  and  12 
Ibs.  of  juice;  hence  taking  into  account  the 
composition  of  the  juice  as  above  given,  the 
22  Ibs.  of  bagasse  consist  of  10.2  Ibs.  moisture 
+  1.2  Ibs.  sugar +0.6  Ibs.  molasses+io.o  Ibs. 
fiber. 

Similarly,  the  composition  of  bagasse  for 
other  degrees  of  extraction  may  be  computed, 
then  reduced  to  percentages  by  weight  of  the 
bagasse  itself,  per  following  table : 


EXTRACTION 

75%  78%         80% 


•or 


Moisture    .      .      .      .51 

Sugar 6 

Molasses    ....   3 
Fiber 40 


46-37  42.5 

5-45  5-° 

2-73  2.5 

45-45  5°-° 


Numerous  experiments  have  shown  the 
calorific  value  of  the  fiber  contained  in  cane 
to  be  about  8,325  B.  T.  U.  per  pound  of  fiber; 
hence  to  obtain  the  calorific  value  of  diffusion 
bagasse  per  short  ton  of  cane,  use  the  formula 

B.  T.  U.  per  short  ton  of  cane=  [27] 

2000X8325 X%  of  Fiber 
100 

Obviously  the  formula  gives  only  the  heat 
generated  by  the  bagasse,  and  not  the  heat 
available  for  steam  generating.  All  moist- 
ure must  be  evaporated  and  the  result- 
ing vapor  be  superheated  to  the  temperature 
of  the  stack  gases.  The  heat  so  absorbed 
must  be  deducted  from  that  calculated  from 
the  formula,  to  determine  the  available  heat. 


122 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


TABLE  38 
FUEL  VALUES  OF   ONE  POUND  OF  DIFFUSION  BAGASSE 


Moisture  in 
Bagasse. 
Per  Cent. 

Heat  Developed  Per 
Pound  of  Bagasse. 
B.  T.  U. 

Heat  Available  Per 
Pound  of  Bagasse 
B.T.U. 

Pounds  of  Bagasse 
Equivalent  to  i  Pound 
of  Coal  Containing 
14,000  B.T.U. 

Estimated  Tem- 
perature of  Fire. 
Fahr. 

o 

8,325 

8,325 

1.68 

2,465° 

20 

6,660 

6,420 

2.18 

2,294 

3° 

5,82) 

5,468 

2.56 

2,186 

40 

4,995 

4,5l6 

3.10 

2,049 

50 

4,162 

3,563 

3-93 

1,870 

60 

3-33° 

2,611 

5-4i 

1,627 

70 

2,497 

1,658 

8.44 

1,281 

75 

2,081 

£.183 

11.90 

i,°45 

TABLE  39 

VALUE  OF    ONE   POUND    OF    MILL  BAGASSE   AT   DIFFERENT    EXTRACTIONS 
UPON  CANE  OF  10  PER  CENT.  FIBRE,  AND  JUICE  CONTAINING 
15   PER  CENT.  SOLID  MATTER 


PER   CENT. 

FIBER. 

SUGAR. 

MOLASSES. 

PKR   CENT. 

EXTRACTION  OF 

MOISTURE    IN 

WEIGHT  OF 

BAGASSE 

PER    CENT. 

FUEL   VALUE 

PER  CENT. 

FUEL  VALUE 

PER  CENT. 

FUEL  VALUE 

CANE. 

IX     BAGASSE 

B.   T.    U. 

IN     BAGASSE 

B.   T.    U. 

IN    BAGASSE 

B.   T.   U. 

(i) 

(a) 

(.0 

(4) 

(s) 

(6) 

(7) 

(8) 

9° 

o.oo 

100  .00 

8,325 

85 

28.33 

66.67 

5,550 

3-33 

240 

i'.67 

116 

80 

42.50 

50  .00 

4,162 

5.00 

361 

2.50 

'74 

75 

51  .00 

40  .  oo 

3,33° 

6  .  oo 

433 

"2    .  OO 

209 

70 

56.67 

33-33 

2,775 

6.67 

482 

3-33 

232 

65 

60  .  71 

28.57 

2,378 

7-J5 

516 

3-57 

248 

60 

63-75 

25.00 

2,081 

7-50 

541 

3-75 

261 

55 

66  .  i  2 

22.22 

1,850 

7.78 

562 

3-88 

270 

5° 

68.00 

2O  .  OO 

1,665 

8.00 

578 

4.00 

278 

45 

69-55 

18.18 

1,513 

8.18 

591 

4.09 

284 

40 

70.83 

16.67 

1,388 

8-33 

601 

4.17 

290 

25 

73-67 

'3-33 

I  ,  I  I  O 

8.67 

626 

4-33 

301 

75-0° 

11.77 

980 

8.82 

637 

4.41 

307 

0 

76.50 

IO  .  OO 

832 

9.00 

650 

4-5° 

TOTAL  HEAT 

HEAT  REQUIRED 

HEAT  AVAIL- 

POUNDS BAGASSE 

PER  CENT. 
EXTRACTION  OF 
WEIGHT  OF 

DEVELOPED 
B.   T.   U. 
SUM  OF   COLUMNS 

TO   EVAPORATE 

THE   WATER 
PRESENT. 

ABLE  FOR 
STEAM  GEN- 
ERATION. 

REQUIRED    TO 
EQUAL   I    LB.  COAL 
CONTAINING 

COAL  EQUIV- 
ALENT PEH 
TON  OF  CANE. 

TEMPERATURE 
OF  FIRE. 

CANE 

4,  6   AND  8. 

B.    T.    U. 

B.   T.   U. 

14,000   B.  T.   U. 

POUNDS. 

FAHH. 

(o) 

do) 

(n) 

(12) 

(M) 

(14) 

90 

8,325 

8,325 

1.68 

119 

,4650 

ST 

5,900 

339 

5,561 

2-52 

119 

,236 

80 

4,697 

509 

4,188 

3-34 

120 

,023 

75 

3,972 

6n 

3,361 

4.17 

120 

,862 

7° 

3-489 

679 

2,810 

4.98 

120 

,732 

65 

3,142 

727 

2,415 

5.80 

121 

,612 

60 

2,883 

764 

2,119 

6.61 

121 

,513 

55 

2,682 

792 

T.Sgo 

7.40 

121 

,427 

5° 

2,521 

815 

1,706 

8.21 

122 

.350 

45 

2,388 

833 

i,555 

9  .00 

122 

,284 

40 

2,279 

849 

i,43° 

9-79 

123 

,222 

25 

2,037 

883 

I>1  54 

12.13 

124 

,077 

15 

1,924 

899 

1,025 

13.66 

124 

,OO2 

0 

1-795 

916 

879 

1  5  •  93 

126 

906 

VARIETIES   OF    PETROLEUM 


123 


Table  38  contains  data  relating  to  the  heat 
developed,  available  heat,  etc.,  per  pound  of 
diffusion  bagasse  of  different  contents  of 
moisture,  assuming  the  temperature  of  the 
air  as  80°  F.  and  that  of  the  stack  gases  as  420°. 
Reference  thus  far  to  the  calorific  value  of 
bagasse  has  been  confined  to  dtffusionbagas.se. 
In  the  diffusion  process  the  cane  is  chopped 
into  small  pieces  and  subjected  to  a  series  of 
soaking  processes,  and  the  resulting  bagasse 
contains  only  fiber  and  moisture.  Mill- 
bagasse  is  the  refuse  left  after  the  cane  has 
been  passed  through  the  rolls.  Not  all  of 
the  juice  is  extracted,  and  the  bagasse  contains 
.  fiber,  moisture  and  juice.  The  juice  contains 
combustible  matter,  viz.,  sugar  and  molasses. 
The  composition  of  the  bagasse  will  vary 
according  to  the  per  cent,  extraction,  as  above 
shown.  According  to  Dr.  Atwater  the  calorif- 
ic value  of  sugar  is  7,223  B.  T.  U.  per  lb.,  and 
that  of  molasses  (dry  matter  only)  is  6,956 
B.  T.  U.  per  lb.  Thus  a  pound  of  mill- 
bagasse  has  a  calorific  value  of 

8,325  X%  Fiber+7,22jX  %  Sugar+6,056  X%  Molasses    r2§~| 

100 

and  its  available  heating  value  will  be  this 
amount,  less  the  B.  T.U.  's  necessary  to  drive 
off  the  contained  moisture. 

Table  39  gives  data  pertaining  to  mill- 
bagasse  of  various  extractions.  Coal  of 
14000  B.  T.  U.  per  pound  is  taken  as  a 
standard,  and  the  coal  ratios  are  obtained 
by  dividing  14000  by  the  available  heat  per 
pound  of  bagasse.  Coal  equivalents  per  ton 
of  cane  are  obtained  by  dividing  the  number 
of  pounds  of  bagasse,  resulting  from  the 
several  extractions,  by  the  coal  ratio.  Thus 
with  an  extraction  of  75%  there  are  500  Ibs. 
of  bagasse  per  (short)  ton  of  cane,  and  500 
^-4.17  (the  coal  ratio  for  75%  extraction)  = 
120  pounds  of  coal,  or  the  coal  equivalent. 
The  coal  equivalents  are  practically  the  same 
for  all  degrees  of  extraction;  in  other  words, 
sugar  cane  has  an  almost  constant  heating 
value,  irrespective  of  how  much  juice  is 
extracted  from  it.  As  the  extraction  grows 
less  there  is  a  greater  weight  of  bagasse  per 
ton  of  cane,  and  while  a  great  part  of  this 
weight  is  due  to  water  and  is  therefore  non- 
combustible,  the  amount  of  juice  left  over  is 
also  greater  and  this  contains  combustible 
matter  which  more  than  compensates  for  the 
additional  water  present.  Thus  the  coal 


equivalent  of  cane  per  ton  actually  increases 
as  the  degree  of  extraction  grows  less. 

A  difficulty,  however,  is  that  large  quan- 
tities of  moisture  render  it  difficult  to  burn 
the  bagasse  except  in  special  furnaces. 
As  the  content  of  moisture  increases  the 
temperature  of  the  fire  decreases,  and  there 
is  danger  of  a  point  being  reached  where 
the  gases  from  the  fuel  will  refuse  to  ignite. 
In  Table  39,  the  highest  attainable  temp- 
erature resulting  from  the  combustion  of 
dry  bagasse  is  2,465°  F.,  and  of  bagasse  of 
75%  extraction  only  1862°  F.  The  cal- 
culations are  made  on  a  basis  of  a  pound 
of  fiber  requiring  i2§  Ibs.  of  air;  sugar, 
9!  Ibs.,  and  molasses,  9^  Ibs.;  which  are 
twice  the  theoretical  amounts  for  complete 
combustion.  The  methods  of  burning  bag- 
asse will  be  treated  in  chapter  on  Fuel 
Burning. 

Corn  is  used  as  a  fuel  in  some  states  when 
the  crop  is  very  abundant  and  the  selling 
price  is  low. 

The  following  are  calorimeter  tests  of 
various  samples  of  corn: 

TABLE  40 
CALORIFIC  VALUE  OF  CORN     (Richards] 


HEATING  VALUE  IN  B.  T.  U. 


MATERIAL. 

PER  POUND 

PER  POUND 

PER  POUND 

OF 

OF  DRY 

OF  DRY 

MATERIAL. 

MATERIAL. 

COMBUST- 

IBLE. 

Yellow 

Dent    Corn  and  Cob 

8,040 

" 

" 

8,202 

8,959 

9,085 

White 

Cob     .      .      . 
Corn  and  Cob 

7,214 
7,841 

7,841 

7,958 

" 

Corn   . 

8,382 

9.199 

9,301 

Cob     .      .      . 

7.571 

8,174 

8,285 

Petroleum  is  practically  the  only  oil 
which  is  sufficiently  abundant  and  cheap 
to  be  used  as  a  fuel  under  boilers.  It  pos- 
sesses many  advantages  over  solid  fuels, 
and  its  use  is  on  the  increase. 

Gasoline,  Benzine,  Kerosene,  and  other 
liquid  oils  distilled  from  petroleum  are 
excellent  fuels,  but  are  too  costly  for  use 
under  boilers.  The  residuum  after  these 
have  been  distilled  off  is  valuable  as  fuel. 

There  are  three  kinds  of  petroleum  in 
use,  namely  those  which  on  distillation 
yield;  (i)  Paraffin;  (2)  Asphalt;  (3)  Olefin. 
To  the  first  group  belong  the  oils  of  the 
Appalachian  Range  and  middle  West.  They 


124 


THE    STIRLING    WATER-TUBE   SAFETY   BOILER 


are  dark  brown  with  greenish  tinge.  Upon 
distillation  they  yield  such  a  variety  of 
light  oils  that  their  value  is  too  great  to 
permit  their  general  use  as  fuels. 

To  the  second  group  belong  the  oils  from 
California  and  Texas.  These  vary  from 
reddish  brown  to  jet  black,  and  are  used 
mostly  for  fuel. 

The  third  group  comprises  oils  from 
Russia,  which  are  also  used  more  extensively 
for  fuel  than  for  any  other  purpose. 


contracts  for  purchase  of  oil  should  limit 
the  content  of  water,  else  sufficient  tankage 
should  be  provided  to  enable  most  of  the 
water  to  be  settled  out  of  the  oil  before  it  is 
burned.  A  large  content  of  water  also 
causes  trouble  with  the  burners. 

Gasoline  Test — The  content  of  water  in 
fuel  oil  is  often  determined  as  follows:  A 
burette  or  other  tall  vessel  provided  with 
glass  stopper  and  graduated  into  200  divis- 
ions is  filled  to  the  100  mark  with  gasoline 


TABLE  41 
CALORIFIC   VALUE    OF   CALIFORNIA    OILS 


Per  Cent 

Per  Cent 

Specific 

Per  Cent 

CALORIFI 
B.   T.   U. 

C   VALUE, 
PER  LB. 

KIND  OF  OIL. 

of 
Sulphur. 

of 

Silt. 

Gravity 
at  60°  F. 

of 
Moisture. 

Oil  as 
Fired. 

Oil  Freed 
of  Water. 

Whittier      

°-975 

0.031 

0.9417 

i  .  06 

18,428.4 

18,626 

1  * 

°-735 

O  .  OIO 

0.9430 

i  .  06 

18,478.8 

18,677 

*  * 

I  .010 

o  .  024 

o  .  9410 

•74 

18,567.0 

18,705 

1  ' 

o  .  960 

0.010 

0.9407 

.42 

18,578.7 

18,657 

Whittier  and  Los  Angeles  mixed 

0.980 

0.054 

0.9530 

4-93 

17,791.2 

18,714 

"         i'ii         ii              i  ( 

°-955 

o  .  048 

0.9529 

4  .  62 

17,887.5 

18,754 

it         ii     1  1         ii              ii 

0.845 

0.032 

0.9637 

8.71 

16,904.  7 

18,518 

ii          i  i     ii          ii              ii 

o  .  840 

o  .  024 

o  .  9629 

8.82 

16,956  .  o 

18,596 

••          "      •         "              " 

A       CA 

17,862  5 

18  607 

•i                ii         ii              ii 

4.^6=; 

I  7  ,830  .  O 

18,692 

,<     <i 

4.    2  ? 

17,074.    C 

18,772 

ii           in         11              ii 

3.6? 

l8,O?Q  .  O 

18,710 

Los  Angeles     

Q  oo 

I  7  ,O3  C  .  O 

18,610 

o  87 

17,122  o 

18  007 

i< 

Q  .  l6 

17,241  .  o 

18,970 

,. 

8   47 

16,980  .  o 

18,551 

,. 

7     S  5 

18,  T,  c6  o 

iQ,8  c  ? 

Kern  Valley     

2.66 

10,410  .0 

IQ  ,o  =;o 

Fullerton    

2     O7 

19,686  .  o 

20,102 

In  general,  crude  oils  consist  mostly  of 
hydrogen  and  carbon,  but  contain  small 
percentages  of  sulphur,  nitrogen,  arsenic, 
phosphorus,  and  silt.  They  also  contain 
a  content  of  water  varying  from  less  than 
one  per  cent,  up  to  50  per  cent.,  depending 
upon  the  care  that  has  been  taken  to  sep- 
erate  out  the  water  which  accompanies 
the  oil  when  pumped  from  the  well.  Here 
as  in  all  other  fuels,  the  percentage  of  water 
affects  the  available  heat  of  the  oil,  hence 


It  is  then  filled  to  the  200  mark  with  the  oil 
to  be  tested,  which  has  first  been  slightly 
warmed.  The  two  are  thoroughly  shaken 
together;  any  shrinkage  below  the  200  mark 
is  made  up  by  adding  more  oil,  and  the 
whole  is  then  allowed  to  stand  in  a  warm  place 
(sometimes  on  an  engine  cylinder)  for  24 
hours.  The  water  and  dirt  settle  to  the 
bottom,  and  the  number  of  divisions  of  each 
give  their  respective  percentages,  by  volume, 
of  the  total. 


FLASH    POINT    OF    OILS 


125 


Flash  Point  142°  F. 
Burning  Point  181°  F. 
Cold  test  6°  F. 


Prof.  James  E.  Denton  gives  the  following 
data  as  a  result  of  his  experiments  with 
Beaumont  (Texas)  crude  oil: 

Carbon         84.60%     Sulphur        1.63% 
Hydrogen    10.90%     Specific  I 
Oxygen          2.87%     Giavity' 

The  Stirling  Company  has  made  various 
tests  on  boilers  fired  with  California  oil, 
samples  of  which  were  subjected  to  calori- 
meter test,  with  results  as  shown  in  Table  41 . 

Table  43  gives  composition  and  calorific 
value  of  some  oils  as  compiled  from  various 
sources. 

The  nitrogen  in  petroleum  varies  from  .  008 
to  1.10%  while  that  of  sulphur  varies  from 
•°  to  %- 


TABLE  43 
COMPOSITION    AND    CALORIFIC    VALUES    OF    VARIOUS    OILS 


Calorific  Value  of  Petroleum— Accurate 

data  on  this  subject  are  scarce.  A  pound 
of  oil  free  of  water  is  usually  considered  to 
have  a  calorific  value  of  from  18,500  to 
22,000  B  T.  U.  Assuming  the  ultimate 
analysis  of  an  average  sample  as  Carbon 
84%,  Hydrogen  14%,  Oxygen  2%,  and 
allowing  for  the  combination  of  the  oxygen 
with  its  equivalent  of  hydrogen  to  form 
water,  the  composition  becomes  Carbon,  84%, 
Hydrogen,  13  .  75%,  Water,  2.  25%;  and  the 
heat  value  per  pound  of  petroleum,  free 
from  water,  is 

Carbon     .      .84     X  14,600=12,264    B.  T.  U. 

Hydrogen      .1375X62,100=  8,625     B.  T.  U. 

Total,   20,889    B.  T.  U. 


KIND  OF   OIL. 

Per  Cent  of 
Carbon. 

Per  Cent  of 
Hydrogen. 

Per  Cent  of 
Oxygen. 

Specific 
Gravity. 

B.  T.  U 

per  pound. 

Heavy  Oil    West  Virginia 

82    c 

I  3  .  3 

T.  .  2 

0.873 

Light  Oil,  West  Virginia 
Heavy  Oil,  Pennsylvania 
Light  Oil    Pennsylvania 

84.3 
84.9 
82   o 

14.1 

J3-7 
14.8 

1.6 
i  .  04 

3  .  2 

0.8412 
0.886 
0.816 

21240 
19224 

Oil  from  Beaumont,  Texas  . 

86   8 

I  T.  .  O 

O  .  O 

o  .  920 

Oil  from  California 

84  o 

12.7 

I  .  2 

O  .  Q2O 

Canada  Crude 

84.   T, 

1^.4 

2  .  3 

20410 

Ohio  Crude 

80     2 

17     I 

2  .  7 

21600 

Oil  from  Parma,  Italy 

84  o 

IT.  .  4 

1.8 

0.786 

Oil  from  Hanover,  Germany 

80.4 

12  .  7 

6.9 

o  .  802 

Oil  from  Galicia,  Austria 
Light  Oil  from  Baku,  Russia 
Heavy  Oil  from  Baku,  Russia    . 
Refuse  of  Oil  "       "           "   .      . 
Oil  from  Java        

82.2 

86.3 

86.6 
87.1 
87.1 

12  .  I 
I3.6 
12.3 
II.7 
12  .O 

5-7 

0.  I 

i  .  i 

I  .  2 

o  .  g 

0.870 
0.884 
0.938 
0.928 
0.92^ 

18416 
22628 
19440 
22628 

The  analysis  and  calorific  value  of  the 
principal  crude  and  residuum  oils  given  by 
Mr.  Orde  are: 

TABLE  42 
ANALYSES     OF     OILS 


CARBON. 

HYDROGEN. 

OXYGEN,   ETC. 

B.  T.  U. 

% 

% 

% 

Per  Ib. 

Texas     .      .      . 

85.66 

II  .03 

3-31 

19,240 

Borneo  . 
Caucasus 

87.8 
84.94 

10.78 
1  3  .  p6 

1.24 
1.25 

18,830 
18,610 

Burmah 

86.4 

12.  I 

i.  5 

18,865 

The  Flash  Point  is  the  temperature  at 
which  an  oil  gives  off  inflammable  gases. 
The  flash  points  of  the  various  oils  are  not 
given  in  the  tables;  in  fact,  data  upon  this 
subject  are  scarce.  In  general  the  light 
oils  have  a  low  flash  point,  while  the  heavy 
grades  have  a  much  higher  flash  point. 
This  matter  is  of  the  utmost  importance 
in  determining  the  availability  of  oil  as  a 
fuel.  The  flash  points  of  oils  whose  specific 
gravities  are  below  0.85  are  generally  below 
60°  F.,  while  those  of  oils  whose  specific 
gravity  exceeds  0.85  are  usually  above 


126 


THE    STIRLING   WATER-TUBE    SAFETY    BOILER 


60°  F.  There  are,  however,  many  ex- 
ceptions to  this  rule,  notably  a  certain 
Roumanian  oil,  whose  specific  gravity  is 
0.899,  an(i  whose  flash  point  is  240°  F.  The 
danger  of  explosion  increases  as  the  flash 
point  is  lowered,  and  the  utmost  care  should 
be  taken  to  lessen  the  possibility  of  the 
light  vapors  becoming  ignited.  When  proper 
precautions  are  taken  the  use  of  oil  is  almost 
as  safe  as  the  use  of  coal. 

Gravity  of  Oils — Fuel  oils  are  often 
valued  according  to  their  gravity  as  indi- 
cated on  the  Beaume  hydrometer,  but  the 
gravity  is  by  no  means  an  accurate  measure 
of  the  relative  calorific  value. 

Petroleum  as  Compared  with  Coal — 
Petroleum  possesses  the  following  advan- 
tages over  coal: 

(1)  Much    lower    cost    for    handling,    as 
the  oil  is  fed  by  simple,  mechanical  means, 
and   cost   of   stoking,    removing   ashes,    etc., 
is  eliminated. 

(2)  For    equal    heat    value    oil    occupies 
less  space  than  coal,  and  the  storage  space 
may   be   at   considerable   distance   from   the 
boilers  without  detriment. 

(3)  Higher  boiler  efficiencies  and    capac- 
ities are  obtainable,  because  the  combustion 
is    more    perfect;    the    excess    air    supply    is 
greatly   lessened;    the    furnace    can   be    kept 
at  constant  temperature  because  fires  do  not 
require    cleaning    nor    furnace    doors    to    be 
opened    for    firing;    smoke    can    be    wholly 
eliminated,   and  the  boiler  heating  surfaces 
do  not  quickly  foul  with  soot. 

(4)  Intensity   of  the  fire   can  be   almost 
instantly  regulated  to  conform  to  the  demand 
for  more  or  less  steam. 

(5)  Oil   does   not,   like    coal,    deteriorate 
with  age  when  stored. 

(6)  Great   reduction   in   number   of   men 
necessary    around    the    plant,    and    freedom 
from  dust,  dirt  and  smoke,  with  their  damage 
to  adjoining  property. 

The  disadvantages  of  oil  are: 

(1)  It   must   have   a   high   flash   point  to 
minimize  danger  of  explosions. 

(2)  City  or  town  ordinances  may  impose 
onerous    conditions    regarding  location   and 
isolation  of  oil  tanks. 

(3)  The    boiler   repair   bill    will    be    high 
unless  the  boiler  is  specially  adapted  to  use 
of    oil.     Whenever    unatomized    oil    strikes 


the  boiler  surface,  a  burn,  blister,  or  bag 
is  almost  sure  to  form,  and  in  boilers  of  the 
tubular,  or  Scotch  Marine  type,  such  bag- 
ging may  cause  a  serious  explosion.  Owing 
to  the  intense  temperature  in  the  fire-box, 
local  overheating  and  burning  of  plates 
are  also  common  in  boilers  which  are  either 
deficient  in  circulation  or  deposit  scale 
on  their  hottest  surfaces.  Constriction  of 
circulation  will  also  inevitably  cause  "steam 
pockets"  which  rapidly  burn  out  the  tubes. 
For  these  reasons  certain  types  of  boilers 
which  seem  fairly  well  adapted  to  use  of 
coal  need  excessive  repairs  when  fired  with 
oil. 

Many  tables  have  been  published  which 
purport  to  show  the  number  of  barrels 
of  oil  equivalent  to  a  ton  of  coal,  and  vice 
versa.  For  example,  assuming  a  barrel  of 
oil  to  weigh  310  Ibs.,  and  a  pound  of  oil 
to  contain  20,000  B.  T.  U.,  the  following 
table  can  be  computed. 

TABLE  44 
COMPARISON  OF  OIL  AND  COAL 


B.  T.   U.    PER   LB. 
OF  COAL. 

LBS.  OF  COAL 
EQUAL  TO    ONE 
BARREL  OF  OIL. 

BARRELS  OF  OIL  EQUAL 
TO    ONE    SHORT  TON 
OF  COAL. 

IO,OOO 
I  I  ,OOO 
12,000 

620 

564 
5J7 

3-23 

3-55 
3-87 

I3,OOO 

477 

4.19 

I4,OOO 
I5,OOO 

443 
4i3 

4.52 
4.84 

This  and  all  similar  computations  based 
upon  the  relative  calorific  power  of  petro- 
leum and  coal  are  of  no  practical  value,  for 
the  reason  that  when  burning  oil,  an  effi- 
ciency ranging  as  high  as  83%  can  be  ob- 
tained with  large  boilers  of  good  design, 
while  with  poorer  grades  of  coal  and  smaller 
boilers  the  efficiency  may  fall  to  65%  or  lower. 
The  efficiency  of  either  fuel  will  depend  upon 
the  size  of  the  boilers,  the  adaptation  of 
their  grates  and  furnaces  to  the  particular 
fuel  used,  the  degree  of  intelligence  of  the 
men  in  charge,  and  other  similar  factors. 
Table  45,  reproduced  from  Power,  January 
1905,  takes  into  account  different  boiler  effi- 
ciencies, but  it  assumes  a  -fixed  calorific  value 
for  oil,  18,500  B.  T.  U.,  hence  this  table  like 


COMPARISON   OF    OIL    AND   COAL 


127 


others  of  similar  nature,  while  very  useful  as  a 
rough  guide,  cannot  enable  one  to  compute  the 
saving  possible  by  substituting  one  fuel  for 
the  other.  The  reason  for  this  is  as  follows : 


The  saving  to  be  made  may  depend  upon  the 
labor  which  can  be  dispensed  with,  the 
available  space  for  fuel  storage,  and  facilities 
for  conveying  the  oil  by  a  pipe  line,  the 


TABLE    45 

EQUIVALENT  HEAT  VALUES  OF  COAL  AND  FUEL  OIL,  ALSO  FACTORS  FOR 

THE  REDUCTION  OF  PLANT  ECONOMY  PER  POUND  OF  COAL 

TO  EQUIVALENT  FIGURES  PER  GALLON 

AND  BARREL  OF  FUEL  OIL 


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POUNDS  OF  WATER  EVAPORATED  PER  POUND  OF  COAL   PER  HOUR 

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POUNDS    OF    OIL     EQUAL      TO     ONE 

BARRELS     OF     OIL      EQUAL     TO     ONE 

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POUND    OF    COAL 

TON     OF     COAL 

ffi 

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z 

z  • 

70 

66 

12  .  64 

4247 

•  3955 

•  4746 

.5538 

•  6329 

.  71  20 

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.8702 

•9493 

2.354 

2.825 

3-296 

3-767 

4.238 

4.709 

5-175 

5-651 

71 

67 

12.83 

4311 

.3897 

.4676 

.6235 

.7014 

•  7794 

.8573 

•  9353 

2.319 

2.783 

3-248 

3.711 

4-  175 

4.  640 

5-103 

5-567 

72 

68 

13.02 

4375 

.3840 

.4608 

.5376 

.6144 

.  69!  2 

.7680 

.8448 

.9216 

2.285 

2.742 

3-  200 

3-657 

4.114 

4-572 

5-028 

5-485 

73 

69 

13.  21 

4439 

-3785 

.4542 

•  5299 

.6056 

.6813 

•  7570 

.8304 

.9084 

2.  252 

2.703 

3-  154 

3-605 

4-054 

4.506 

4-956 

5.406 

74 

70 

13-40 

4502 

•  3731 

-4477 

-5224 

.5970 

.6716 

.7462 

.8208 

.8955 

2.  221 

2.665 

3-ioS 

3.554 

3-998 

4-442 

4-887 

5-331 

75 

71 

13.60 

.3676 

.4411 

.5147 

.5882 

.66l8 

•  7352 

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2.188 

2  .  626 

3.064 

3.501 

3-939 

4-377 

4-8   5 

5-  252 

76 

72 

13-79 

4633 

-3625 

-4350 

.5076 

.5801 

.6526 

•  7251 

.7976 

.8702 

2.  158 

2.589 

3.022 

3-453 

3-885 

4-317 

4.748 

5-180 

77 

73 

13-98 

4697 

-3576 

.4291 

.5007 

.5722 

.6437 

•  7153 

.7868 

.8583 

2  .  129 

2.555 

2  .  980 

3.406 

3-832 

4.258 

4.683 

5  •  lot) 

78 

74 

14.  17 

476i 

-3528 

•  4234 

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•  5645 

.6351 

-7057 

.7762 

.8468 

2  .  100 

2  .  520 

2.941 

3-360 

3.78o 

4.  200 

4.621 

5.041 

79 

75 

14.36 

4825 

•  3481 

.4178 

.4874 

.5571 

.  6267 

.6963 

.  7660 

•  8352 

2.072 

2.487 

2.907 

3-3i6 

3.731 

4-  145 

4-559 

4-974 

80 

76 

14-55 

4889 

-3436 

•  4123 

.4811 

-5498 

.6l85 

.6872 

.7560 

•8247 

2.045 

2.454 

2.863 

3-272 

3.682 

4.090  4-499 

4.909 

VALUES     OF    H 

VALUES    OF    J 

70 

66 

12  .64 

4247 

.0494 

.0593 

.0692 

.0791 

.0890 

.0988 

.    087 

.    187 

849.5 

707.8 

606.  7 

530.8 

471.8 

424.7 

386.0 

353-9 

67 

12.83 

43  I  i 

.0487 

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.0682 

.0779 

.0877 

.0974 

.    071 

.    169 

862.2 

716.5 

615.8 

538.8 

478.8 

431  -0 

391  -9 

359-2 

72 

68 

13.02 

4375 

.  0480 

•  0576 

.0672 

.0768 

.0864 

.  0960 

.    056 

•    152 

875-0 

729.  I 

625  .0 

546.9 

486.0 

437-5 

397-6 

364.5 

73 

69 

13.21 

4439 

.0473 

.0568 

.0662 

.0757 

.0853 

.0946 

.    038 

.    136 

887.8 

739-8 

634.1 

554-9 

492.0 

443-9 

403-4 

369-9 

74 

70 

13.40 

4502 

.0466 

-0559 

.0653 

.0746 

.0839 

.0932 

.    026 

.    119 

900.4 

750.3 

643.  i 

562.7 

500.  2 

450.2 

409.2 

375-1 

75 

71 

13.60 

4569 

•  0459 

-0551 

.0643 

-0735 

.0827 

.0919 

.      01  I 

.    103 

913.8 

761.5 

652.7 

571- 

507.6 

456.9 

4I5-3 

380.7 

76 

72 

13-79 

4633 

-0453 

•  0544 

.0635 

.0725 

.O8l6 

.0906 

.0997 

.    088 

926.  6 

772.1 

661.8 

579- 

514.7 

463-3 

421  .  i 

386.0 

77 

73 

13.98 

4697 

.0447 

-0536 

.0626 

-0715 

.0805 

.  0894 

.0983 

•    073 

939-4 

782.8 

671  .0 

587. 

521.8 

469.  7 

426.4 

391  -4 

78 

74 

14.17 

476i 

-0441 

.0529 

.0617 

.0705 

•  0794 

.0882 

.0970 

•    059 

952  .  2 

793  •  5 

680.  i 

595- 

529.0 

476.  i 

432.8 

396.7 

79 

75 

14.36 

4825 

-0435 

.0522 

.  0609 

.0696 

-0783 

.0870 

.0957 

•    044 

965.0 

804.  i 

689.3 

603. 

536.1 

482.5 

438.6 

402  .0 

80 

76 

14-55 

4889 

.0429 

.0515 

.0601 

.0687 

.0773 

.0859 

-  1945 

.    031 

977-8 

8:4.8 

698.4 

611  . 

543-2 

488.9 

444-4 

407-4 

Net  efficiency  is  determined  by  deducting  from  boiler  efficiency  4  per  cent.,  representing 
steam  used  for  oil  burners  and  oil  pumps. 

One  ton  of  coal  weighs  2,000  pounds.     One  barrel  of  oil  weighs  336  pounds.     One  gallon 
of  oil  weighs  8  pounds.     One  pound  of  oil  contains  18,500  B.T.U. 

Equivalent  gallons  of  oil  per  kilowatt  hour=  HXpounds  of  coal  per  kilowatt  hour. 

J 


Equivalent  kilowatt  hours  per  barrel  of  oil  = 


pounds  of  coal  per  kilowatt  hour. 


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128 


COMPARISON  OF  NATURAL  GAS  AND  COAL 


129 


hours  per  day  the  plant  operates,  and  the 
quantity  of  coal  needed  for  banking  fires, 
the  possibility  of  operating  an  oil  fired  plant 
where  a  coal  fired  plant  would  be  objection- 
able owing  to  smoke,  and  many  other  sim- 
ilar considerations,  far  more  than  on  the 
relative  calorific  value  of  oil  and  coal.  In 
consequence  there  is  but  one  reliable  method 
of  determining  the  relative  advantages  of 
the  two  fuels,  and  that  is  by  operating  the 
plant  with  each  fuel  for  an  interval  of  time 
long  enough  to  give  accurate  data  regarding 
costs  of  every  item  entering  into  the  problem. 
Any  other  method  must  necessarily  be 
approximate  to  such  a  degree  as  to  render 
it  practically  guesswork. 

Coal  Tar  usually  has  a  value  for  other 
purposes  far  exceeding  its  fuel  value,  yet 
at  times  it  is  used  to  advantage  for  fuel. 
It  differs  from  crude  oil  chemically,  being 
lower  in  hydrogen  and  higher  in  carbon, 
and  therefore  of  a  lower  calorific  value. 
The  following  is  an  ultimate  analysis  of  a 
tar  made  from  a  standard  gas  coal : 

Carbon 89  .  2 1  % 

Hydrogen 4.95 

Nitrogen I-°5 

Oxygen 4.20 

Ash .06 

Sulphur 53 

B.  T.  U.  per  pound.       .    15,388 

Water=Gas  Tar  is  lighter  than  coal  tar, 
and  is  the  residuum  of  gas  oil.     Its  analysis 
is  as  follows: 

Carbon  .      .      .      .      .      .      92 . 70% 

Hydrogen   .      .      .      .      .        6. 13 

Nitrogen o .  1 1 

Oxygen 0.68 

Ash 05 

Sulphur  .33 

B.    T.    U.  per    pound,    .     17,296 

A  gallon  of  coal  tar  weighs  10.33  Ibs., 
and  a  gallon  of  water-gas  tar  9.58  Ibs.  In 
actual  tests  the  former  has  evaporated  11.91 
Ibs.  of  water  per  pound  of  fuel,  and  the  latter 
14.9  Ibs.,  from  and  at  212°. 

Natural  Gas  is  pumped  from  the  wells  to 
the  point  where  it  is  to  be  used.  The  gas 
leaves  the  pumping  station  in  the  field  at 
pressures  reaching  250  pounds  per  square 
inch;  at  the  receiving  station  it  is  reduced 


to  a  pressure  of  4  to  5  pounds  before  entering 
the  distributing  mains.  At  the  boiler  house 
this  pressure  is  still  further  reduced  by  a 
valve  controlled  by  the  steam  pressure. 
The  final  pressure  at  which  the  gas  enters 
the  burner  is  usually  measured  by  a  mercurial 
pressure  gauge  graduated  to  read  in  pounds 
and  ounces  per  square  inch.  The  charge 
for  gas  is  based  upon  readings  of  a  meter 
placed  between  the  reducing  valve  and  the 
burner.  For  purposes  of  comparison  all 
observations  should  be  based  on  gas  re- 
duced to  standard  temperature  of  32°  F. 
and  absolute  atmospheric  pressure  of  14.7 
Ibs.  per  square  inch.  When  the  temper- 
ature and  pressure  corresponding  to  the 
meter  readings  are  known,  the  volume  of 
gas  under  standard  pressure  and  temper- 
ature can  be  obtained  by  multiplying  the 
number  of  cubic  feet  indicated  on  the  meter 

by   - — - —  in    which    P=    absolute    pressure 

in  pounds  per  square  inch,  and  T  absolute 
temperature  F.  of  the  gas  at  the  meter.  In 
boiler  tests  the  evaporation  should  be  re- 
duced to  that  per  cubic  foot  of  gas  under 
standard  pressure  and  temperature. 

The  weight  of  natural  gas  is  about  45.6 
Ibs.  per  i  ,000  cubic  feet  under  standard 
conditions.  The  composition  varies  con- 
siderably, even  in  the  same  field.  Table  45 
gives  analyses  and  calorific  values  of  natural 
gases  from  various  localities. 

Comparison  of  Natural  Gas  and  Coal 
— The  same  reasons  which  present  any  accu- 
rate comparison  of  the  value  of  coal  and 
petroleum  without  an  actual  test  apply  with 
equal  force  in  case  of  coal  and  natural  gas. 
The  following  table,  based  upon  the  assump- 
tion that  one  cubic  foot  of  gas  under  standard 
conditions  will  evaporate  .75  Ib.  of  water, 
will  enable  an  approximate  comparison  to 
be  made. 


WATER  EVAPORATED 
PER  POUND  OF  COAL 

7 
8 

9 

10 
ii 


NO.  OF  M  CU.  FT.  GAS 
EQUAL    2,000   LBS.  COAL 


21.3 

24.O 

26  .  7 
29-3 


Natural  gas  at  6  cents  per  1,000  cubic 
feet  will  be  equal  in  heating  value  to  coal 
which  evaporates  7  Ibs.  of  water  per  pound 
and  costs  $1.12  per  ton. 


REPUBLIC    IRON   &   STEEL   CO.     YOUNGSTOWN,  O.,  OPERATING    1  1  ,3OO    H.   P.  OF  STIRLING    BOILERS 


Determination  of  Heating  Value  of  Fuels 


Methods  —  The  heating  value  of  a  fuel 
may  be  determined:  (i)  By  calculation 
from  a  chemical  analysis:  (2)  By  burning  a 
sample  in  a  calorimeter.  In  the  first  method 
the  calculation  may  be  based  on  either  an 
ultimate  ana  y sis  or  a  proximate  analysis. 
An  ultimate  analysis  reduces  the  fuel  to 
its  elementary  constituents  of  carbon,  hy- 
drogen, oxygen,  nitrogen,  sulphur,  and  the 
ash  and  moisture.  The  work  requires  the 
services  of  a  chemist,  and  for  further  par- 
ticulars the  reader  is  referred  to  Stillman's 
Engineering  Chemistry.  A  proximate  anal- 
ysis determines  only  the  per  cent,  of  fixed 
carbon,  volatile  matter,  moisture,  and  ash, 
but  does  not  determine  the  ultimate  com- 
position of  the  volatile  matter. 

Caution  in  Interpreting  Results  of  Ul- 
timate Analyses — Reports  of  ultimate  an- 
alyses sometimes  give  the  percentages  of 
constituents  referred  to  weight  of  the  sample 
less  its  weight  of  moisture.  When  the 
report  gives  the  proportions  in  this  way 
and  also  the  per  cent,  of  moisture  originally 
in  the  sample,  the  true  analysis  can  easily 
be  obtained,  as  shown  in  following  case: 


CHEMIST  S        TRUE 
REPORT      ANALYSIS 


Carbon 
Hydrogen . 
Oxygen 
Nitrogen    . 
Sulphur 
Ash      .      . 

Moisture    . 


76.91 

72.25 

5-°7 

4.76 

8.65 

8.125 

1.16 

i  .09 

I  .  21 

i  .  135 

7  .00 

6.58 

100.00 

6.06 

6.06 

106.06        100.00 


The  true  analysis  is  obtained  by  dividing 
each  of  the  apparent  percentages,  as  reported, 
by  the  sum,  106.06. 

The  per  cent,  of  moisture  determined  by 
drying  a  large  sample,  immediately  after 


it  is  taken  from  the  coal  pile,  will  almost 
invariably  be  larger  than  determined  from 
the  analysis,  because  in  shipping  the  sample 
to  the  chemist,  and  preparing  it  for  analysis, 
some  of  the  moisture  evaporates. 

The  ultimate  analysis  resolves  the  fuel 
into  its  elementary  constituents  but  does 
not  reveal  how  these  may  have  been  com- 
bined in  the  fuel.  The  manner  of  their 
combination  undoubtedly  affects  the  cal- 
orific value,  as  fuels  yielding  identical  ul- 
timate analyses  often  give  different  heating 
values  when  tested  in  a  calorimeter.  The 
difference  is  very  slight,  and  a  very  close 
approximation  to  the  heating  value  may 
be  computed  from  the  ultimate  analysis. 

Calculations  from  an  Ultimate  Analy= 
sis — The  first  formula  for  the  calculation  of 
heating  values  from  the  composition  of  a  fuel 
is  due  to  Dulong,  and  this,  slightly  modified, 
is  used  to-day.  Other  formulas  have  been 
proposed,  some  of  which  give  more  accurate 
results  for  particular  classes  of  fuels,  but 
most  of  them  are  based  upon  Dulong 's 
and  are  merely  modifications  of  it.  Du- 
long's  formula*  converted  into  British  Units 
is 

Heating  value  in    B.  T.  U.  per  lb.= 

14,500  C+62,ioo  j  H—  [29] 

(  8  ) 

The  coefficients  14,500  and  62,100,  repre- 
senting the  heat  of  combustion  of  carbon 
and  hydrogen,  have  been  investigated  by 
numerous  experimenters  who  determined 
values  which  differ  slightly  from  those 
above  given.  With  a  view  of  establishing 
some  uniform  practise  the  American  So- 
ciety of  Mechanical  Engineers,  in  their 
"Rules  for  Conducting  Boiler  Trials, "  Code 
of  1899,  recommend  the  following; 

Heating  value  in  B.  T.  U.  per  lb.= 

14,600(7  +  6  2,000  \H—   ->-+4,oooS       [24] 
(          8    ) 


*Dulong's  original  formula  in  French  units  is 

Heat  Value   in  Calories  =8080^  +  3  4,500^  H  -  —  i  [30] 

f  O       ) 

The  calorie  is  the  heat  unit  of  the  metric  system,  and  when  used  as  a  measure  of  the  heating  value  of 
fuel,  it  is  the  number  of  units  of  weight  of  water  which  may  be  heated  one  degree  Centigrade  by  the  com- 
bustion of  one  unit  weight  of  coal.  The  unit  of  weight  may  be  either  a  kilogram,  gram  or  pound.  When 
thus  used  a  calorie  is  equivalent  to  1.8  B.  T.  U. 


132 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


C,H,0,  and  5  are  the  proportional  content  ot 
carbon,     hydrogen,     oxygen,     and     sulphur, 


formula  gives   results    nearly   identical  with 
those  obtained  from  calorimetric    tests,  and 


respectively.     This     formula   is  generally  ac-      may  safely  be  applied  to  all  solid  fuels    ex- 


cepted    by    all    American     Engineers.     The 
last    term   represents    the    heating    value    of 


cept  cannel  coal,  lignite,  turf  and  wood,  when- 
ever  a  correct  ultimate  analysis  is  available. 


100 


0610 

PERCENTAGE  OF  HYDROGEN 

FIG.  25       CHART    ILLUSTRATING    MAHLER'S    FUEL   FORMULA 

sulphur,  based  on  determinations  made  by  Mahler's    Formula*  is    based  upon  the 

Lord.     The  method  of  using  the  formula  has  content   of   carbon   and   hydrogen   only.     It 

already  been  shown  on  page:  06.  is    simpler    than    Dulong's,    and    sufficiently 

The   investigations   of    Mahler   in    France,  accurate  for  many  practical  purposes.     It  is: 

Lord  and   Haas  in  this  country,  and  Bunte  B.  T.  U.  per  pound  of  fuel= 

in    Germany,     all    show    that    the     Dulong  201  C  +  676  #-5540                  [31] 

*For  derivation  of  this  formula  see  The  Locomotive,  November,  1903. 


WEIGHT  AND    CALORIFIC    VALUE    OF    GASES 


133 


in  which  6"  and  H  are  the  percentages  by 
weight,  of  carbon  and  hydrogen  in  the 
fuel.  An  advantage  of  this  formula  is  that  the 
results  may,  without  calculation,  be  obtained 
from  the  diagram,  Fig.  25.  Example:  To 
find  the  calorific  value  of  a  fuel  containing 
four  per  cent,  hydrogen,  eighty-four  per- 
cent, carbon,  and  twelve  per  cent,  of  ash, 
water,  etc.,  locate  on  the  hydrogen  scale  at 
the  bottom  the  line  under  four;  pass  ver- 
tically upward  along  this  line  until  it  inter- 
sects the  horizontal  line  passing  through 
eighty-four  on  the  carbon  scale.  The  point 
of  intersection  is  on  the  line  marked  14,000, 
hence  the  fuel  contains  14,000  B.  T.  U.  per 
pound. 


Heat  Values  of  Gaseous  Fuels— The 
method  of  computing  calorific  values  from 
ultimate  analyses  is  particularly  adapted  to 
solid  fuels,  with  the  exceptions  already  noted. 
In  the  case  of  gaseous  fuels,  it  is  better  to 
separate  trfem  into  their  elementary  con- 
stituent gases,  and  to  compute  the  heating 
values  of  these  gases  separately.  Usually 
only  hydrogen,  carbon  monoxide  (CO)  and 
certain  hydrocarbons  will  be  found  constitut- 
ing the  combustible  portion  of  the  gas. 
Table  47  gives  calorific  value  of  the  com- 
monest combustible  gases. 

Application  of  the  table.  As  gas  analyses 
may  be  reported  either  by  weight  or  by  vol- 
ume, an  example  of  each  will  be  given: 


TABLE  47 

WEIGHTS  AND  CALORIFIC  VALUE  OF  GASES  AT  32°  F. 
AND  ATMOSPHERIC  PRESSURE 


GAS. 

Chemical 
Symbol 

Cubic  Feet 
per    Pound 
of  Gas. 

B.  T.  U. 
per  Pound 
of  Gas. 

Cu.  Ft.  of  Air* 
Required  per 
Pound 

B.  T.  U. 
per  Cubic  Foot 
of  Gas. 

Cu.  Ft.  of  Air 
Required  per 
Cubic  Foot 

of  Gas. 

of  Gas. 

Hydrogen   . 

H                178.93 

62,000 

428.25 

346 

2-39 

Carbon  Monoxide 

CO                12.  81 

4,35° 

30.60 

339 

2-39 

Marsh  Gas 

CH4              22.43 

23>564 

214  .  oo 

1050 

9-54 

Acetylene    . 

C2H2 

13-79 

21,465 

164.87 

!556 

11  -93 

Olefiant  Gas     . 

C2H, 

I  2.  80 

21,440 

183.60 

1675 

14.33 

Ethane        .      .      . 

C2H6 

11.96 

22,230 

199.88 

1859 

16.72 

*To  reduce  volumes  of  air  to  pounds  of  air  multiply  by  12.39. 


Correction  for  Hydrogen,  Moisture 
and  Nitrogen  —  If  the  fuel  contains  water,'  the 
heat  necessary  to  evaporate  it  and  to  super- 
heat the  steam  thus  formed  produces  no 
useful  result  and  should  be  deducted  from 
the  amount  given  by  the  above  formulas. 
The  same  thing  applies  to  the  water  formed 
from  the  hydrogen  present.  The  nitrogen 
in  the  fuel  absorbs  heat  without  producing 
any  benefit.  The  total  losses  due  to  these 
causes  can  be  computed  by  the  formula 

B.  T.  U.  Lost= 

(9  H  +  W)  [212.9  -*  +  965-8  +  0.48  (tc-2i  2)] 

[32] 


In  which  H,  W,  and  N  are  the  proportional 
content  of  hydrogen,  water  and  nitrogen, 
/c  the  temperature  of  breeching,  and  /  the 
temperature  of  air  supply. 


(1)  A    blast    furnace    gas,     analysis    by 
weight  being,  oxygen  (O)=  2.7;  carbon  mon- 
oxide    (CO)  =  19. 5;    carbon    dioxide    (CO2) 
=  18.7;  nitrogen  (N)  =  59  .  i ;  all  in  per  cents. 
The    only    combustible    present     is    carbon 
monoxide,  hence  the  heating  value  per  pound 
of  the   gas  is  0.195X4350=848.25   B.   T.    U. 
The  net  volume  of  air  needed  to  burn  a  pound 
of  the  gas  is  0.195X30.6=5.967  cu.  ft. 

(2)  A    natural    gas,   analysis    by    volume 
being,   oxygen   (0)=o.4o;    carbon    monoxide 
(CO)=o.95;  carbon  dioxide   (CO2)=o.34;  ole- 
fiant    gas     (C2H4)=o.66;    ethane    (C2H6)= 
3.55;    marsh    gas    (CH4)  =  72.i5;    hydrogen 
(H)=2i.95,    aU    m    Per  cents.     All  but  the 
0  and  CO3  are  combustibles,  hence  the  heat 
developed   and   net   air  required   per  pound 
of  gas  will  be  as  worked  out  in  detail  in  the 
following  table: 


ANALYSIS  OF  ALABAMA  COALS 


135 


Heat  from  CO     =0.0095X339    =      3.22 

C2H  =0.0066X1675=    11.05 

"     C'H, =o. 0355X1859  =    65.99 

C  H.=o. 7215X1050=757. 58 

H  =0.2195  X    346  =    75.95 


B.    T.    U. 


Total, 


9J3-79 


B.     T.    U 


Air  needed  for  CO  =o.oo95X  2.39  =  0.022705^.  ft. 
"  C2H.,  =0.0066  X  14.33  =0.094578 Cu.  ft. 
'  C,HG  -0.0355  X  16.72  =o.59356oCu. ft. 
"  C  H4  =0.7215  X  9.54=6.883iioCu.ft. 
"  H  =o.2i95X  2.39  =0.524605  Cu.ft. 


Total  air  needed, 


8.118558  Cu.  ft. 


Proximate  Analysis  —  The  proximate 
analysis  of  fuel  gives  its  proportions  of  fixed 
carbon,  volatile  combustible  matter,  moisture 
and  ash.  It  is  made  by  subjecting  a  sample 
to  a  temperature  of  250°  to  300°  to  expel 
the  moisture,  then  to  a  red  heat  which  expels 
the  volatile  matter;  then  to  a  white  heat 
which  causes  the  carbon  to  pass  off  as  dioxide, 
leaving  the  ash  as  a  residue.  By  weighing 
the  residue  at  end  of  each  operation  the 
various  percentages  can  be  computed.  See 
Article  XV  of  Code,  in  chapter  on  Rules  for 
Conducting  Boiler  Trials,  page  204. 

Table  48  gives  ultimate  and  proximate 
analyses  of  Alabama  coals,  and  illustrates 
the  relationship  between  the  two. 

The  proximate  analysis  is  easy  to  make, 
it  affords  information  as  to  the  general 
characteristics  of  a  fuel ,  and  its  relative  heat- 
ing value,  but  from  it  the  heating  value  can- 
not be  directly  computed.  The  reason  is 
that  the  volatile  content  varies  widely  in 
composition  and  heating  value. 


Comparison  of  many  experiments  has 
resulted  in  production  of  some  methods  of 
estimating  the  calorific  value  of  coals  from 
proximate  analyses.  Kent*  deduced  from 
Mahler's  tests  on  European  coals  the  ap- 
proximate heating  values  of  coal  dependent 
upon  the  content  of  fixed  carbon  in  the 
combustiblef  as  given  in  the  following  table. 

TABLE  49 

APPROXIMATE  HEATING  VALUE  OF  COALS 
(Kent.) 


Percentage 
Fixed  Carbon 
in  Coal  Dry 
and  Free  from 
Ash. 

Heating  Value 
B.  T.  U. 
per  Pound 
Combustible. 

Percentage 
Fixed  Carbon 
in  Coal,  Dry  and 
Free  from  Ash. 

Heating  Value 
B.  T.  U. 
per  Pound 
Combustible. 

IOO 

14,600 

68 

I5'48o 

97 

14.940 

63 

15,120 

94 

15,210 

60 

14,580 

9° 

15,480 

57 

14,040 

8? 

i  5,660 

55 

13.320 

So 

15,840 

53 

12,600 

72 

15,660 

51 

12,240 

Example:  Given  a  coal  whose  proximate 
analysis  is,  fixed  carbon  6 1  %,  volatile  matter 
29%,  ash  8%,  moisture  2%.  The  com- 
bustible portion  amounts  to  61  +  29=90% 
of  which  the  fixed  carbon  is  61^-90=68%. 
From  Table  49  the  combustible  portion  of 
such  a  coal  has  a  heat  value  of  15,480  B. 
T.  U.;  hence  the  correct  heating  value,  per 
pound  of  coal,  is 

i5,48oX. 90=13, 932  B.  T.  U. 


TABLE  48 
PROXIMATE  AND  ULTIMATE  ANALYSES  OF  ALABAMA  COALS 


Common  to  Proxi- 

Proximate Analyses. 

Ultimate  Analyses. 

mate  and  Ultimate 

Analyses. 

Name  of  Seam, 

Location. 

Volatile 

and  Com- 
bustioie 

Fixed 
Carbon. 

Carbon. 

Hydrogen 

Oxygen. 

Nitrogen. 

Sulphur. 

Ash. 

Moist- 
ure. 

Matter. 

Wadsworth 

Helene 

34-3° 

60.50 

73-23 

7.98 

11.92 

.07 

0.  60 

3-5° 

.70 

Pratt 

Pratt 

33-45 

63.20 

75.82 

10.52 

7-51 

-73 

1.07 

2  .  00 

•35 

Brookwood 

Brookwood 

27.80 

58.70 

72-47 

10.38 

I  .  60 

0.40 

1.65 

I  I  .90 

.60 

Woodstock 

Bloc  ton 

34.80 

60  .  60 

72-75 

8.61 

11.12 

.48 

1.44 

2.65 

•95 

Underwood 

Blocton 

35-65 

57-3° 

70.82 

10.19 

9-95 

•31 

0.68 

5-25 

.80 

Pratt 

Pratt 

3x-55 

64-95 

75-05 

9.91 

8-95 

.62 

0.97 

2-35 

•  J5 

Milldale 

Brookwood 

3°  -5° 

66.30 

73-96 

10.50 

'9-57 

.62 

I-I5 

2  .  2O 

.  00 

Blue  Creek 

25.80 

69  .  90 

72.68 

10.77 

9-83 

!-39 

i  .03 

2.80 

•  5° 

Coalburg 

32-55 

65-57 

74-59 

10.58 

9.48 

i-3i 

1.32 

I  .  90 

.82 

Cahaba 

3°-  T5 

52.90 

60.37 

10.70 

9.00 

i  .  26 

1.72 

16.30 

•65 

*  Steam  Boiler  Economy,  First  Edition,  p.  47. 


fSee  foot-note,  page  112. 


28,000 


27,000 


26,000 


25,000 


24,000 


23,000 


22,000 


21  ,000 


20,000 


19,000 


18,000 


17,000 


16,000 


15,000 


14,000 


10  15  20  26  30  36  40  45  50 

PER  CENT  OF  VOLATILE  IN  THE    COMBUSTIBLE. 
FIG.  26.     GOUTAL'S   VALUES    FOR  "A"   IN    B.  T.  U.=  1 4.76O  C +aV 


GOUTAL'S    FORMULA    FOR    CALORIFIC   VALUE    OF   COAL 


137 


To  facilitate  the  use  of  Kent's  method, 
Fig.  27  has  been  prepared;  the  per  cent,  of 
fixed  carbon  in  the  combustible  having  been 
located  on  the  abscissa,  the  B.  T.  U.  per 
pound  of  combustible  can  be  determined 
from  the  corresponding  ordinate. 

Goutal*  gives  carbon  a  fixed  value,  and 
considers  the  heat  value  of  the  volatile 
matter  a  function  of  its  percentage  referred 
to  combustible.  Goutal's  formula,  in  Brit- 
ish units,  is, 


v+c 


05 

.  10 


•25 
•30 
•35 
•38 
.40 


2  6 , 1 OO 

23.400 

21  ,060 
19,620 
18,540 
17,640 
16,920 

15.300 
I4,4OO 


16,000 


15,500 


i5,OOO 


14,500 


14,000 


13,500 


13,000 


12,500 


55  60  65  70  75  80  85 

PER  CENT  OF  FIXED  CARBON  IN    COMBUSTIBLE. 


90 


95 


FIG.  27.     GRAPHICAL  REPRESENTATION   OF  THE   RELATION   BETWEEN   PERCENTAGE  OF  FIXED  CARBON 
IN   COMBUSTIBLE,   AND  THE  CALORIFIC  VALUE   PER   POUND  OF  COMBUSTIBLE 


B.  T.  U.  per  Ib.  of  coal=  i4,j6oC-\-aV      [33] 
In  which 

C=  the  proportional  content  of  fixed  car- 
bon in  the  coal. 

V=  the  proportional  content  of  volatile 
matter  in  the  coal. 

a=  a  variable  depending  on  the  ratio  V 
of  volatile  matter  to  combustible, 
per  following  table,  or  from  Fig.  26. 


Applying  the  formula  to  the  same  coal  as 
in    preceding    example,    6"=o.6i;    ^=0.29; 

o .  29 

V'= =  .3 2,  hence  from  the  figure"  a "  = 

.6i+.29 

17,300,  hence  B.  T.  U.  per  pound  of  coal  = 
14,760X0.61  +  17,300  Xo.  29  =  14, 020,  which 
is  only  about  six-tenths  of  one  per  cent, 
different  from  the  value  found  by  Kent's 
method. 


*Comptes  rendus  de  V Academie  des  Sciences,  Vol.  cxxxv,  p.  477. 


138 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


Illinois  Coals  —  From  calorimetric  de- 
terminations and  chemical  analyses  of  over 
a  thousand  samples  of  coal,  R.  W.  Hunt 
&  Co.,  deduced  the  formula, 

B.  T.    U.   per   pound  of   coal= 

14, 544  C+i6, 515^—  io,ooo.4          [34] 

which  is  correct  within  narrow  limits  for  Illi : 
nois  coals  in  which  the  content  of  fixed  carbon 
and  volatile  matter  ranges  from  40  to  45  per 
cent.;  when  the  ash  lies  between  10  to  15 


FIG.  28  FIG.  29 

PARR'S   FUEL  CALORIMETER 

per  cent,   the  formula  will  be  more  accurate 
if  written. 

B.  T.  U.  per  pound  of  coal= 
14,544(^+16,515^+354/1-1635         [35] 

In  both  cases  C,  V,  and  A  are  the  pro- 
portional content  of  fixed  carbon,  volatile 
matter,  and  ash. 

Range  of  Accuracy  of  Fuel  Formulas- 
Mr.  Kent  states  that  for  coals  containing  sixty 
per  cent,  or  more  of  fixed  carbon  in  the  com- 
bustible, the  values  in  Table  49  are  prac- 
tically correct,  but  for  coals  containing  less 


than  sixty  per  cent,  of  fixed  carbon  the 
tabular  values  are  liable  to  an  error  of  four 
per  cent,  in  either  direction 

M.  Goutal  states  that  his  formula  proved 
very  accurate  over  a  wide  range  of  exper- 
iments, six  hundred  different  coals  being 
used,  and  that  the  error  rarely  exceeded  one 
per  cent. ;  it  was  found  to  give  values  two  per 
cent,  high  for  some  anthracites  and  lignites. 

So  far  as  the  present  writer  has  been 
able  to  test  these  two  methods,  they  give 
results  which  are  accurate  enough  for  all 
ordinary  work,  when  applied  to  eastern 
coals  whose  percentage  of  fixed  carbon  and 
volatile  matter  fall  within  their  range,  but 
they  apply  with  less  accuracy  in  propor- 
tion as  the  coals  are  mined  in  the  fields  far- 
ther to  the  west,  and  for  fuels  mined  in 
Wyoming,  Colorado  and  farther  west  and 
north  the  formulas  are  of  little  use.  Con- 
sequently, while  fuel  formulas  are  of  great 
value  where  approximate  results  only  are 
necessary,  a  calorimetric  determination  of 
the  heating  value  of  the  fuel  is  necessary 
whenever  exact  results  are  required. 

Calorimetry — The  ultimate  or  proximate 
analysis  of  a  fuel  is  useful  in  determining 
its  general  character,  and  in  making  a  close 
approximation  to  its  heating  value;  but 
for  a  practical  determination  of  heating 
value  the  calorimeter  method  is  more  sat- 
isfactory. In  this  a  sample  of  the  fuel 
is  actually  burned,  and  the  heat  of  com- 
bustion is  measured. 

Calorimeters  are  composed  of  a  com- 
bustion chamber  and  a  calorimeter  bath, 
the  latter  consisting  of  a  vessel  surrounding 
the  combustion  chamber,  and  containing 
a  known  quantity  of  water.  The  elevation 
of  the  temperature  of  the  water,  when 
accurately  measured  and  multiplied  by  suit- 
able constants  peculiar  to  the  apparatus, 
determines  the  heating  power  of  the  fuel. 

Mahler's  Calorimeter  is  very  popular' 
and  much  used,  but  its  operation  is  very 
complicated,  and  requires  an  expert.  Both 
the  instrument  and  method  of  operating 
it  are  described  in  Kent's  Steam  Boiler 
Economy. 

Parr  Calorimeter — A  very  reliable,  in- 
expensive, and  simple  calorimeter  is  that  in- 
vented by  Prof.  S.  W.  Parr,  of  the  University 
of  Illinois.  This  apparatus  does  not  require 


PARR'S   FUEL   CALORIMETER 


139 


the  services  of  an  expert  operator.  Oxygen 
is  not  used,  no  high  pressures  are  employed, 
and  the  total  time  consumed  in  conducting 
a  test  on  a  weighed  and  dried  sample  should 
not  exceed  15  or  20  minutes. 

Fig.  28  shows  the  relative  position  of  parts. 
The  can  A  is  filled  with  two  litres  of  water. 
The  combustion  takes  place  within  the  car- 
tridge D.  The  resulting  heat  is  imparted  to 
the  water.  The  rise  in  temperature  is  in- 
dicated by  the  finely  graduated  thermometer 
T.  Fig.  29  shows  the  cartridge  in  which  is 


Extraction  of  the  heat  is  complete  in  from 
four  to  five  minutes.  The  maximum  reading 
is  taken  and  the  rise  in  temperature,  multi- 
plied by  a  simple  factor,  gives  the  heat  in 
British  thermal  units  per  pound  of  coal.  By 
a  slight  modification  of  the  apparatus,  igni- 
tion may  also  be  effected  by  an  electric  fuse, 
and  where  current  is  available  this  method 
is  preferred  by  some  users. 

The  instrument  is  well  adapted  to  the  de- 
termination of  sulphur  in  coal,  pyrites,  pe- 
troleum, etc.  Upon  dissolving  out  the 


ST.  CLAIR   STEEL   COMPANY,  CLAIRTON,   PA.,  OPERATING   6.50O   H.  P.  OF  STIRLING   BOILERS 


placed  a  weighed  quantity  of  coal,  previously 
ground  to  pass  through  a  100  mesh  sieve  and 
dried  in  the  usual  way  at  220°  to  230°  F. 
There  is  also  put  into  the  cartridge  a  chem- 
ical compound  which  is  thoroughly  mixed 
with  the  coal  by  shaking.  The  cartridge  is 
then  placed  into  a  measured  quantity  of  water 
in  the  insulated  calorimeter  can  A.  The 
stirrer  is  set  in  motion  and  operated  by  a 
cord  about  the  pulley  P.  After  a  constant 
temperature  has  been  attained  ignition  is 
effected  by  means  of  a  short  piece  of  hot  wire 
dropped  through  the  stem  of  the  cartridge. 


products  of  combustion  from  the  bomb  the 
sulphur  of  the  original  material,  being  in 
the  form  of  soluble  sulphate,  may  very 
readily  be  made  to  indicate  the  percentage 
content  by  a  simple  photometric  device. 

The  residue  from  the  combustion  contains 
the  carbon  of  the  coal  in  the  form  of  sodium 
carbonate.  The  volume  of  carbon  dioxide 
may  readily  be  measured,  and  from  this  the 
total  carbon  of  the  coal  can  be  calculated. 
This  is  a  result  not  heretofore  available 
except  by  ultimate  analysis,  and  enhances 
the  value  of  the  instrument. 


Fuel  Burning 


The  preceding  chapter  indicates  the  wide 
range  of  the  nature  and  calorific  value  of  the 
available  boiler  fuels ;  the  methods  of  burning 
these  fuels  to  best  advantage  will  now  receive 
attention. 

Draft — The  intensity  of  draft  required 
varies  with  the  kind  and  amount  of  fuel  to 
be  burned  per  square  foot  of  grate,  as  shown 
by  Fig.  38*  in  the  chapter  on  Chimneys.  It 
is  well  known  that  if  the  draft  is  deficient,  the 
volatile  matter  in  the  fuel  escapes  unburnt 
with  the  furnace  gases,  and  the  fire  is  dead  and 
smoky.  It  is  not  generally  recognized  that 
an  excess  of  draft  causes  equally  large  losses 
by  burning  holes  through  the  fire  and  ad- 
mitting surplus  air  which  reduces  the  furnace 
temperature.  Consequently,  to  secure  the 
most  efficient  results  the  draft  should  be 
regulated  by  the  damper  to  just  the  amount 
corresponding  to  the  desired  combustion 
rate,  and  no  more. 

Anthracite  may  be  burned  in  almost  any 
kind  of  furnace,  but  the  grate  area,  and 
the  intensity  of  draft  must  be  sufficient  to 
burn  the  amount  of  coal  requisite  to  develop 
the  desired  capacity.  When  possible  the 
coal  should  be  at  least  6  inches  deep  on  the 
grates,  because  with  thinner  fires  air  holes 
are  liable  to  form  in  the  bed  of  coals.  The 
smaller  sizes  of  anthracite  require  more  draft 
than  the  larger  sizes,  and  the  light  weight  of 
the  coal  particles  renders  it  difficult  to  pre- 
vent the  draft  forcing  holes  through  the  fuel. 
If  a  thick  fire  is  maintained  so  as  to  avoid  an 
excess  of  air,  the  tendency  of  the  fuel  is  to 
choke  the  interstices  in  the  grate-bars  and  to 
cause  a  deficit  of  air.  To  keep  between  these 
limits  and  obtain  just  the  correct  amount  of 
air  requires  considerable  skill  on  the  part  of 
the  fireman.  The  fires  require  frequent 
cleaning,  and  as  the  size  of  the  coal  decreases 
there  is  likely  to  be  trouble  from  clinkers. 

The  successful  burning  of  these  small  sizes 
requires  a  grate  with  a  large  number  of  very 
small  air  openings,  and  usually  forced  draft. 
When  the  coal  clinkers  a  steam  jet  blowing 
into  the  ash  pit  will  be  found  beneficial. 
Shaking  grates  may  also  be  used  to  advan- 
tage, since  they  make  it  possible  to  rid  the 

*See  page  174.  , 


fires  of  ash  without  disturbing  them  to  any 
great  extent  on  the  surface.  Once  anthracite 
is  placed  into  the  furnace  it  should  not  again 
be  touched  except  when  it  is  necessary  to  clean 
the  fire. 

In  proportion  as  the  coal  is  coarser,  more 
of  it  may  be  fired  at  each  charge.  The  proper 
interval  between  charges  can  be  determined 
by  careful  observation  of  the  fire.  After  the 
fire  reaches  a  white  heat  the  lower  part  of  the 
bed  of  coals  will  burn  away,  and  the  upper 
surface  will  sink;  this  sinking  indicates- 
the  proper  moment  for  firing  again  be- 
cause unless  fresh  coal  is  quickly  added, 
air  holes  will  form  in  the  fire.  In  one  or 
two  minutes  after  the  new  charge  of  coal  is 
fired,  flame  will  appear  over  this  coal  in 
in  spots  which  indicate  uneven  flow  of  air 
through  the  fuel.  These  spots  should  im- 
mediately be  covered  with  additional  fresh 
coal  so  spread  as  to  compel  the  air  to  pass 
at  a  uniform  rate  through  the  entire  bed  of 
fuel.  No  further  coal  should  be  thrown 
upon  the  fire  until  it  sinks  again,  otherwise  the 
formation  of  clinkers  will  be  considerably 
increased. 

The  Stirling  furnace  is  perfectly  adapted 
to  anthracite,  and  the  incandescent  arch 
supplies  the  heat  necessary  to  ignite  the  car- 
bon monoxide  distilled  from  the  fresh  coal, 

Volatile  Matter — All  coals  except  anthra- 
cite contain  a  considerable  portion  of  volatile 
matter  which  must  be  burned  to  develop 
the  full  heating  power  of  the  fuel.  How 
to  do  this  has  always  been  a  most  trouble- 
some problem  which  is  seldom  solved  in 
boiler  furnaces.  The  per  cent,  of  volatile 
matter  steadily  increases  in  the  progression 
from  anthracite  to  lignite;  accordingly,  as- 
the  coal  is  of  poorer  grade  not  only  is  its 
calorific  power  less,  but  it  becomes  more 
difficult  to  develop  what  it  has.  The  reason 
for  this  lies  principally  in  the  failure  to  adapt 
the  furnace  to  the  peculiarities  of  the  coal. 

When  fresh  bituminous  coal  is  thrown 
upon  the  fire  "the  first  thing  that  the  fine 
fresh  coal  does  is  to  choke  the  air  spaces 
existing  through  the  bed  of  coke,  thus  shut- 
ting off  the  air  supply  which  is  needed 


142 


THE    STIRLING   WATER-TUBE    SAFETY    BOILER 


to  burn  the  gases  produced  from  the  fresh 
•coal.  The  next  thing  is  a  very  rapid  evap- 
oration of  moisture  from  the  coal,  a  chilling 
process,  which  robs  the  furnace  of  heat. 
Next  is  the  formation  of  water-gas  by  the 
•chemical  reaction,  C+H2O=CO+2H,  the  steam 
being  decomposed,  its  oxygen  burning  the 
carbon  of  the  coal  to  carbonic  oxide,  and 
the  hydrogen  being  liberated.  This  reaction 
takes  place  when  steam  is  brought  in  contact 
with  highly  heated  carbon.  This  also  is  a 
chilling  process,  absorbing  heat  from  the 
furnace.  The  two  valuable  fuel-gases  thus 
generated  would  give  back  all  the  heat  ab- 
sorbed in  their  formation  if  they  could  be 
burned,  but  there  is  not  enough  air  in  the 
furnace  to  burn  them.  Admitting  extra  air 
through  the  fire-door  at  this  time  will  be 
of  no  service,  for  the  gases  being  compara- 
tively cool  cannot  be  burned  unless  the  air 
is  highly  heated.  After  all  the  moisture  has 
been  driven  off  from  the  coal,  the  distillation 
•of  hydrocarbons  begins,  and  a  considerable 
portion  of  them  escapes  unburned,  owing  to 
the  deficiency  of  hot  air,  and  to  their  being 
chilled  by  the  relatively  cool  heating  sur- 
faces of  the  boiler.  During  all  this  time  great 
volumes  of  smoke  are  escaping  from  the 
chimney,  together  with  unburned  hydrogen, 
hydrocarbons,  and  carbonic  oxide,  all  fuel- 
gases,  while  at  the  same  time  soot  is  being 
deposited  on  the  heating  surface,  diminish- 
ing its  efficiency  in  transmitting  heat  to 
water.'  '* 

To  burn  these  gases  it  is  necessary  that 
they  be  brought  into  contact  with  a  supply 
of  air  hot  enough  to  cause  ignition,  and  that 
they  have  ample  space  in  which  to  mix  with 
the  air  and  burn  completely  before  coming 
into  contact  with  the  boiler  surfaces  which  are 
comparatively  cool  and  extinguish  the  flame. 

Inefficient  Furnaces — Few  boiler  fur- 
naces comply  with  these  requirements.  In  the 
internally-fired  boiler  the  furnace  is  surround- 
ed with  water  so  that  the  gases  are  liberated 
in  a  space  which  is  too  restricted  to  permit 
proper  mixture  with  air,  and  too  cold  to 
cause  ignition.  In  the  return  tubular  boiler 
there  is  more  space  available  for  mixing  the 
gases  and  air  but  the  flame  is  extinguished 
by  the  cool  boiler  shell  which  forms  the  top 
•of  the  furnace.  In  the  horizontal  water-tube 
boiler  the  roof  of  the  furnace  is  a  nest  of 


water- tubes,  and  any  flame  not  extinguished 
by  first  contact  with  them  is  extinguished  by 
being  drawn  between  them  and  surrounded 
by  water-cooled  surfaces.  Complete  com- 
.bustion  of  volatile  matter  in  such  boiler 
furnaces  is  therefore  impossible. 

The  Stirling  Furnace  has  already  been 
described,  and  its  adaptation  to  burning 
volatile  matter  set  forth,  f  An  abundant 
supply  of  air  can  be  admitted  to  the  gases  at 
all  times,  and  as  the  furnace  is  surrounded  by 
incandescent  fire-brick  the  heat  necessary  for 
complete  ignition  of  the  gases  is  available  and 
at  the  right  place.  The  distinguishing  feature 
of  the  Stirling  furnace  is  the  fire-arch.  That 
this  is  an  indispensable  part  of  any  furnace 
efficient  for  burning  volatile  matter  is  recog- 
nized by  engineers.  Many  opinions  in  sup- 
port of  this  statement  might  be  quoted,  but 
the  following  must  here  suffice. 

"Chilling  the  gases  before  combustion  is 
complete,  should  be  carefully  prevented; 
and  comparatively  cold  surfaces,  as  those 
of  a  steam  boiler,  should  not  be  placed  too 
near  the  burning  fuel.  A  large  combus- 
tion chamber  should,  where  possible,  be 
provided,  and  more  complete  combustion 
may  be  expected  in  furnaces  of  large  size, 
lined  'with  fire-brick,  and  with  arches  of 
the  same  material,  than  in  a  furnace  of  small 
size  where  the  fire  is  surrounded  by  chilling 
surfaces,  as  in  a  'fire-box  steam  boiler'." 
(R.  H.  Thurston,  A  Manual  of  Steam  Boil- 
ers, yth  ed.,  p.  188.) 

"The  change  required  in  the  furnace  is  the 

roofing  of  it  with  fire-brick "     (Kent, 

Steam  Boiler  Economy,  1901,  p.  159.) 

"Of  all  the  different  kinds  of  furnaces 
designed  for  various  purposes,  the  most 
persistent  smoker  is  that  of  the  steam 
boiler.  The  reason  is  obvious,  for  there 
are  not  hot  walls  to  radiate  back  the  heat 
and  thus  aid  combustion.  In  some  designs 
of  boilers  the  furnace  is  enclosed  in  a  fire- 
brick combustion  chamber,  and  the  products 
are  not  admitted  to  the  heating  surfaces 
until  after  combustion  has  become  more  or 
less  perfect.  This  arrangement  has  met  with 

success   in   many   instances    "     (H. 

De  B.  Parsons,  Steam  Boilers,   1903,  p.   15.) 

Bituminous  Coals  and  Lignites — The 
difficulties  encountered  in  burning  bitu- 
minous coal  with  economy  and  without 


*Kent;  Steam  Boiler  Economy,  p.  155.         fSee  pages  10  and  n. 


THE    COKING   METHOD    OF   FIRING   COAL 


143" 


smoke  increase  as  the  content  of  fixed  carbon 
grows  less;  the  coals  requiring  the  greatest 
skill  in  handling  are  those  of  the  bituminous 
variety  from  Illinois,  Iowa,  Missouri  and 
the  West.  To  burn  the  volatile  matter 
the  furnace  must  be  large,  to  permit  the  air 
and  gases  to  mingle;  hot,  to  ignite  the  mix- 
ture and  complete  the  combustion  before 
he  boiler  surface  is  reached;  and  provided 
with  ample  grate  surface  to  burn  the  requi- 
site quantity  of  fuel — requirements  pre- 
fectly  met  in  the  Stirling  furnace. 

The  fire  needs  more  attention  than  in 
case  of  anthracite.  The  fixed  carbon  will 
usually  take  care  of  itself  if  the  fire  is  so 
handled  as  to  burn  the  volatile  matter. 
The  depth  of  coal  to  be  carried  on  the  grates 
to  produce  the  best  results  varies  through  wide 
limits  according  to  the  nature  of  the  coal. 
Coa's  from  the  same  locality  may  require 
different  depths,  hence  it  is  impossible 
to  give  any  general  rule  applicable  to  all 
cases.  The  fireman  must,  by  careful  trials 
with  each  coal,  determine  the  proper  depth; 
the  following  information  may  serve  as  a 
suggestion  when  making  such  trials. 

Semi-bitumious  coals,  such  as  Pocahontas, 
New  River,  Clearfield,  etc.,  require  fires 
from  12  to  14  inches  thick;  fresh  coal  should 
be  charged  at  intervals  of  10  to  20  minutes, 
and  the  quantity  should  be  sufficient  to 
maintain  the  thicknecs  above  given.  Bi- 
tuminous coals  from  the  Pittsburg  district 
require  fires  4  to  6  inches  deep,  and  should 
be  fired  often  and  in  comparatively  small 
charges.  The  coals  mined  in  Kentucky, 
Tennessee,  Ohio,  and  Illinois  require  a 
depth  of  3  to  4  inches.  Free-burning  coals 
from  Rock  Springs,  Wyoming,  require  6  to 
8  inches,  while  the  poorer  coals  of  Montana, 
Utah  and  Washington  require  a  depth  of 
about  4  inches.  Colorado  lignites  require 
a  depth  of  4  to  6  inches,  and  grates  with 
air  spaces  only  \  to  -j^-inch  wide.  Nova 
Scotia  coals  require  a  large  supply  of  air, 
and  the  bed  of  coals  must  be  so  thin  as 
barely  to  cover  the  grates. 

In  general,  the  coals  mined  in  the  western 
part  of  the  United  States  require  thinner 
fires  than  the  eastern  coals.  If  thicker 
fires  are  carried  the  tendency  to  clinker 
is  increased.  When  burning  these,  fresh  fuel 
should  be  fired  often  and  in  small  amounts. 


With  hand  firing  there  are  three  methods 
of  feeding  the  coal: 

(1)  The     Alternate,  in  which  the  fresh- 
coal  is  fired  on  one  side  of  the  grate  at  a 
time.     The    volatile    matter    distilled    from 
the  fresh   charge   can  be   effectively  burned 
by   the    air   which    is    heated   when    passing 
through   the   other   side;   thus   the   two   im- 
portant   stages    of    coal    burning    are    made 
to    occur   at   once, — the    combustion   of   the- 
volatile  matter,  and  the  burning  of  carbon _ 
This    obviates    the   necessity    of    continually 
altering   the   air   supply   to    correspond   first 
with   one   stage,    and   then   the   other.     The- 
alternate     method     gives     excellent     results 
when  properly  carried  out. 

In  this  method,  and  in  the  spread-firing 
method  next  to  be  described,  the  coal  should 
be  thrown  exactly  where  it  is  wanted,  and 
not  be  further  disturbed  by  poker  or  slice 
bar,  except  when  absolutely  necessary  to' 
clean  fires  or  break  up  clinkers. 

(2)  In  Spread=firing   very  little  fuel    is 
charged  at  one  time,  and  this  is  either  deftly 
spread  over  the  entire  fuel  bed,  or  in  patches. 
Firing   "lightly   and  often"  is    spread-firing 
practically.     Where  the  fuel  is  laid  in  patches- 
some    of    the    advantages    of    the    alternate 
method  are  obtained,  but  it  has  the  disad- 
vantage that  the  entire  grate  must  be  cleaned 
at  one  time.     This  method  is  fairly  successful 
with  small  sizes  of  free-burning  coals  in  fur- 
naces where  the  gases  rise  vertically. 

(3)  The  Coking  Method  consists  of  firing 
the  fresh  coal  to  a  considerable  depth  directly 
in  front  of  the  firing  doors,  and  pushing  it 
back  into  the  furnace  as  soon  as  it  has  coked. 
This  results  in  a  very  hot  fire  in  the  rear  of  the 
furnace,  due  to  burning  carbon,  and  if  the 
volatile  matter  from   the   fresh   coal  passes, 
over  this  highly  heated  portion  the  combustion 
will   be   perfect   provided   the   air   supply   is> 
correct.     This     method    is  not    particularly 
successful    where    the    volatile    matter    rises 
vertically  in  the  boiler,  as  is  the  case  in  hori- 
zontal water-tube  boilers  employing  vertical 
baffles.     In  the  Stirling  the  arched  furnace 
directs  the  gases  horizontally  for  a  considerable 
distance,  and  the  coking  method  has  given 
very  satisfactory  results  with  coals  containing 
a    large    amount    of    volatile    matter.     This 
method  of  firing  was  once  very  extensively 
employed,  but  is  now  going  out  of  use.     A- 


METHODS   OF    BURNING    WOOD 


145 


disadvantage  is  that  air  passes  much  more 
easily  through  the  coked  coal  than  through 
the  fresh  coal,  hence  it  is  necessary  to  main- 
tain a  considerably  greater  depth  of  fuel  on 
the  rear  of  the  grates  than  on  the  front.  The 
fuel  is  also  stirred  up  when  it  is  pushed 
toward  the  rear  of  the  grates,  and  it  is  now 
recognized  that  the  less  the  coal  is  disturbed 
after  it  is  fired,  the  more  efficiently  it  can  be 
burned.  To  use  the  coking  method  success- 
fully the  fireman  must  not  only  possess  con- 
siderable skill,  but  must  also  give  his  undivided 
attention  to  the  work. 

The  best  method  to  adopt  will  depend  upon 
the  character  of  the  fuel,  and  like  all  other 
work  done  by  manual  labor,  on  the  "per- 
sonal equation"  of  the  fireman,  but  there 
should  be  some  method  followed,  and  the  fir- 
ing not  be  done  haphazardly.  A  careful  trial 
of  the  three  methods  will  show  which  one  is 
best  adapted  to  the  conditions,  and  that  one 
should  be  adhered  to.  There  may  be  a  dif- 
ference of  from  10  to  20  per  cent.,  between 
the  results  obtained  from  careless  and  skilled 
firing.  Few  boiler  owners  realize  the  saving 
to  be  effected  by  employing  skilled  and  con- 
scientious firemen. 

Mechanical  Stokers — Of  these  there  are 
two  general  classes: 

(a)     Over-feed.          (b)     Under-feed. 

The  first  spreads  the  fresh  coal  over  the 
fuel  bed,  and  the  second  feeds  it  below  the 
grates,  then  upward,  until  it  overflows  out 
over  the  grates. 

There  are  three  kinds  of  over-feed  stokers 
in  use.  In  one  the  coal  is  carried  on  horizontal 
or  slightly  inclined  grate  bars,  and  the  in- 
dividual bars  are  given  a  mechanical  motion 
by  which  the  coal  is  gradually  advanced 
along  the  grates  toward  the  bridge  wall.  In 
another  the  grates  are  steeply  inclined,  and 
the  fuel  is  pushed  on  to  the  upper  ends, 
whence  it  slides  down  slowly  toward  the  ash- 
pit, burning  in  transit.  The  third  kind 
includes  "chain  grates,"  in  which  the  entire 
grate  is  an  endless  chain  of  short  bars.  The 
motion  is  from  the  fuel  hopper  in  front  of  the 
boiler,  back  toward  the  bridge  wall,  at  which 
point  the  grate  passes  over  a  sprocket,  then 
returns  through  the  ash  pit.  The  Stirling 
Chain  Grate  is  typical  of  this  class. 

Underfeed  stokers  feed  into  a  receptacle 
below  the  grates,  and  the  fuel  gradually  over- 


flows out  onto  the  grates.  It  undergoes  a 
coking  process  in  the  receptacle,  and  should 
be  free  from  all  volatile  matter  when  the 
grates  are  reached.  Some  of  these  stokers 
operate  intermittently,  by  means  of  a  plunger; 
others  feed  continuously  through  a  screw  mo- 
tion and  forced  draft  is  used. 

In  favor  of  mechanical  stokers  it  is  urged 
that  they  reduce  the  cost  of  fire-room  labor, 
cause  a  slightly  increased  evaporation  per 
pound  of  coal,  permit  of  the  use  of  coal-con- 
veying apparatus,  and  lessen  if  not  wholly 
prevent  smoke.  With  the  chain  grate  type 
of  mechanical  stoker,  instead  of  a  higher  rate 
of  evaporation  per  pound  of  coal,  a  positive 
loss  over  hand-firing  may  result  unless  the 
stoker  design  prevents  large  excess  quantities 
of  air.  If  an  analysis  of  the  flue-gases  shows 
100  per  cent,  or  more  excess  air,  steps  should 
be  taken  to  prevent  this  air  from  entering  the 
furnace,  otherwise  the  economy  will  be  greatly 
reduced. 

Any  type  of  mechanical  stoker  purporting 
to  feed  the  fuel  regularly  into  a  properly 
designed  furnace  should  furnish  a  solution  to 
the  problem  of  smokeless  combustion,  since, 
with  uniform  fuel  supply,  and  the  air  under 
control,  it  ought  to  be  possible  to  attain  just 
that  proportion  between  the  two  which  is 
necessary  for  perfect  combustion;  and  once 
having  attained  it,  to  maintain  it.  Practic- 
ally this  degree  of  perfection  is  not  always 
realized,  although  mechanical  stokers  properly 
managed  will  often  give  results  superior  to 
ordinary  hand-firing  both  in  point  of  smoke- 
lessness  and  fuel  economy,  and  permit  use  of 
lower  grades  of  fuel  than  would  be  profitable 
with  hand-firing. 

WOOD. 

The  efficient  burning  of  wood  requires  a 
large  combustion  chamber,  and  grates  ar- 
ranged to  prevent  admission  of  surplus  air. 
The  Stirling  furnace  perfectly  meets  these 
requirements,  and  is  easily  modified  to  suit 
any  kind  of  wood  fuel. 

For  the  burning  of  shavings  and  sawdust, 
chutes  are  arranged  in  the  boiler  front,  and 
feed  the  fuel  directly  upon  the  grates.  Where 
sawmill  refuse  is  conveyed  to  the  boilers  by 
carriers,  a  simple  extension  of  the  furnace  pro- 
vides a  roof  containing  an  opening  through 


GRATES  FOR  BAGASSE  FURNACE 


147 


which  the  refuse  can  be  dropped  automat- 
ically into  the  furnace. 

For  ordinary  air-dried  cord  wood  the  grates 
are  placed  at  firing  floor  level,  their  area  is 
reduced  to  about  two-fifths  the  amount 
required  for  coal,  and  the  furnace  walls, 
beginning  under  the  arch,  are  battered  to 
form  a  V,  with  the  grates  at  the  bottom. 
Cord  wood  to  a  depth  of  30  to  36  inches  can 
be  carried  on  the  grates,  and  the  freshly  fired 
wood  crowds  down  that  which  has  been  partly 
burned,  thus  filling  the  large  interstices  at  the 
bottom  with  burning  coals,  hence  leakage  of 
air  past  the  fire  is  prevented.  When  other 
considerations  prevent  battering  the  furnace 
walls,  the  grates  may  be  lowered  as  before, to 
secure  the  requisite  thickness  of  fire,  and  the 
rear  part  of  the  grates  may  be  blocked  off, 
leaving  in  front  the  area  that  is  desired. 

For  burning  green  cord  wood  and  wet  slabs, 
the  conditions  closely  approximate  those  for 
burning  green  bagasse,  as  described  in  the 
following  article,  and  a  similar  furnace  may 
be  used  for  both. 

The  Stirling  Company  has  worked  out 
many  special  arrangements  of  furnace  for 
burning  wood  fuel  in  various  degrees  of  dry- 
ness,  and  forms  in  which  it  is  delivered  as 
refuse  from  factories  and  mills,  and  is  pre- 
pared to  submit  a  design  to  fit  any  special 
conditions  which  may  arise. 

Tan  Bark,  or  mixtures  of  tan  bark,  sawdust 
and  slabs,  are  burned  perfectly  in  the  Stirling 
bagasse  furnaces.  In  many  cases  such  material 
containing  as  high  as  55  per  cent,  of  moisture 
is  handled  in  this  furnace  with  entire  success, 
and  the  full  rating  of  the  boiler  is  developed 
notwithstanding  the  high  content  of  moisture 
in  the  fuel. 

BAGASSE. 

Effect  of  Moisture — Though  it  has  been 
shown  in  the  chapter  on  Fuels  that  bagasse 
has  practically  a  constant  heat  value  per  ton 
of  the  original  cane,  irrespective  of  the  degree 
of  juice  extraction,  it  does  not  follow  that 
bagasse  of  the  low  extractions  will  produce 
as  much  useful  steam.  To  make  this  more 
clear,  consider  2500  pounds  of  dry  diffusion 
bagasse  burned  beneath  a  boiler,  and  assume 
that  all  of  the  heat  of  the  bagasse  (25ooX 
8325  =  20,812,500  B.  T.  U.)  is  generated  and 
made  available  for  evaporating  water  in  the 

10 


boiler ;  then  with  a  boiler  efficiency  as  low  as 
50%  this  heat  would  evaporate  10,773  pounds 
of  water  from  and  at  212°.  But  if  to  the 
2500  pounds  of  dry  bagasse,  7500  pounds  of 
water  be  added,  the  mixture  will  not  even 
burn  unless  dried  or  mixed  with  large  quan- 
tities of  dry  fuel,  notwithstanding  the  fact 
that  the  heat  in  the  2500  pounds  of  dry 
matter  is  sufficient  to  evaporate  nearly  three 
times  the  7500  pounds  of  water  present. 
Hence  it  is  all  important  how  the  water  is 
present.  When  mixed  with  the  bagasse  (and 
assuming  that  ignition  is  started)  its  evapora- 
tion results  in  the  absorption  of  so  much  of  the 
heat  generated  that  the  surrounding  tem- 
perature is  lowered  to  a  point  at  which  further 
combustion  cannot  take  place,  and  the  fire  is 
extinguished.  If  this  evaporation  can  be 
made  to  occur  apart  from  the  combustion  of 
the  bagasse,  there  will  be  sufficient  heat 
generated  to  evaporate  the  water  content 
and  leave  an  excess  for  useful  work. 

Furnace  Requirements — A  high  furnace 
temperature  must  be  maintained,  and  this 
is  best  accomplished  by  making  the  furnace 
entirely  of  fire-brick  and  locating  it  away  from 
the  boiler  heating  surfaces,  so  that  combustion 
may  be  complete  before  the  boiler  surfaces 
are  reached.  Consequently  an  extension  fur- 
nace, in  conjunction  with  the  Stirling  boiler, 
as  shown  in  Fig.  30,  proves  eminently  satis- 
factory, and  is  a  combination  widely  used 
in  the  cane-sugar  countries. 

Stirling  Green  Bagasse  Furnace — The 
Stirling  furnace  for  green  bagasse  is  a  greatly 
improved  form  of  the  Burt  patent.  It  is 
rectangular  in  shape,  and  is  made  in  various 
widths  and  depths  according  to  the  capacity 
of  the  boiler  and  the  quality  of  the  bagasse. 
The  roof  is  arched  and  the  entire  interior  of 
the  furnace  is  lined  with  fire-brick.  The 
fresh  fuel  is  admitted  through  an  opening  at 
the  top,  being  conveyed  by  a  carrier  to  be 
later  described.  See  Fig.  31. 

Grates — -The  grate  surface  is  composed 
of  Hollow  Blast  Grate  Bars,  alternating  with 
plain  herring-bone  or  straight  ribbed  bars. 
The  hollow  blast  bar  is  a  rectangular  casting, 
provided  with  openings  on  its  upper  face 
which  are  covered  with  a  sliding  plate  known 
as  the  "blast- valve,"  by  means  of  which  the 
air  is  discharged  into  the  furnace  in  nearly 
horizontal  jets,  and  so  directed  that  those  of 


148 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


one  bar  cross  those  of  the  bars  adjacent. 
Thus  the  air  supply  not  only  is  under  perfect 
control,  but  the  manner  of  its  admission  in- 
sures an  excellent  distribution  throughout  the 
mass  of  fuel.  The  alternate  arrangement  of 
hollow  and  ordinary  grate  bars  renders  the 
furnace  capable  of  burning  coal  or  wood  very 
advantageously,  either  with  or  without  forced 
draft. 

Air  from  the  blower  is  led  to  a  cast  iron 
pipe  in  the  ash-pit,  and  from  this  connections 
are  made  to  the  hollow  bars  from  below; 
where  there  are  several  boilers  the  air  supply 
of  each  is  under  separate  control,  permitting 
any  boiler  to  be  operated  independently. 

Advantages — The  fire-brick  walls  and  the 
arch  become  white  hot,  thus  storing  heat, 
which  radiates  upon  and  dries  the  fresh  charge 


plete  shut  down  of  the  plant  one  or  two  hours 
daily.  (2)  The  air  supply  can  be  so  regu- 
lated that  no  excess  over  that  actually  required 
need  be  admitted.  This  greatly  increases  the 
efficiency  of  combustion. 

Stoking  Arrangements — An  important 
feature  where  there  are  several  furnaces  is  the 
bagasse  conveyor,  the  automatic  features  of 
which  contribute  materially  to  the  economy 
of  the  plant.  See  Fig.  31. 

The  conveyor  is  supported  on  a  structural 
steel  framework,  and  runs  in  a  trough  made 
of  steel  plate.  The  carrier  is  composed  of 
endless  chains  fitted  with  bars  which  engage 
the  bagasse  and  convey  it  from  the  mill  to  the 
boilers.  In  the  bottom  of  the  trough  are 
adjustable  openings  through  which  any 
desired  charge  of  bagasse  is  automatically 


FIG.  31.     FRONT  ELEVATION  OF  STIRLING  GREEN    BAGASSE  CONVEYOR   AND   AUTOMATIC   FURNACE  FEEDER 


of  bagasse.  The  moisture  thus  evaporated 
mingles  with  the  highly  heated  gases  from 
the  bagasse  already  in  the  furnace,  and  the 
actual  burning  of  the  fresh  charge  does  not 
begin  until  all  of  its  moisture  has  passed  off. 
The  air  supplied  is  dry  and  the  volatile 
matter  is  burned  at  the  high  temperature 
necessary  for  proper  combustion,  the  whole 
operation  taking  place  before  the  boiler 
heating  surface  is  reached 

The  superior  points  of  this  arrangement 
are :  ( i )  The  discharge  of  the  air  into  the  fuel 
insures  the  combustion  of  the  sugar  and 
molasses  contained  in  it,  and  prevents  forma- 
tion of  clinker.  Where  the  air  is  admitted 
in  any  other  manner,  incomplete  combustion 
occurs,  and  the  sugar  and  silica  form  a  hard 
clinker  which  is  an  endless  source  of  trouble 
frequently  requiring  for  its  removal  a  corn- 


dropped  into  hoppers  set  over  each  furnace. 
The  hoppers  are  fitted  with  valves  operated 
automatically  by  means  of  cams  on  a  shaft 
along  the  boiler  fronts.  Periodically  each 
valve  opens,  then  closes  when  a  charge  of  fuel 
has  passed  into  the  furnace,  very  little  free 
air  being  admitted. 

Excess  Bagasse — Frequently  more  bagasse 
is  discharged  from  the  mill  than  is  required 
at  the  time  for  steam-making;  the  conveyor 
provides  for  this  by  carrying  the  excess 
beyond  the  boilers,  where  it  is  stored  until 
such  times  as  it  is  needed.  It  is  then  con- 
veyed back  to  the  furnace  by  the  same 
carrier.  With  this  system  of  handling  and 
burning  green  bagasse  the  fuel  problem  is 
greatly  simplified,  and  a  sugar-house  can  be 
operated  with  excellent  economy.  The  ap- 
paratus is  practically  automatic,  reducing 


TEST    OF    BAGASSE    FURNACE    UNDER   WORKING    CONDITIONS  149 

TEST   OF   STIRLING   BOILERS   BURNING  GREEN    BAGASSE 

GENERAL   DATA. 

Date  of  test December  26,  1896. 

Duration  of  test  Six  (6)  hours. 

Grate  area,  square  feet 160 

Heating  surf  ace,  sq.  ft 5>75° 

Steam  pressure  ( gauge ) 98.1 

Feed  water 150.5°  F. 

FUEL. 

Kind  of  fuel Bagasse 

Per  cent,  moisture 42.21 

Total  fuel  consumed 67.343  Ibs. 

Total  dry  fuel  consumed f 37»577 

Total  refuse 566 

Total  combustible ." 37.011 

Fuel  burned  per  hour 11,224 

WATER. 

Total  water  apparently  evaporated 153,178  Ibs. 

Total  water  actually  evaporated 150,115 

Equivalent  actually  evaporated  from  and  at  212°  F 165,682 

ECONOMIC   EVAPORATION. 

Water  evaporated  per  pound  of  bagasse  from  actual  temperature  and  pressure  2.23  Ibs. 
Water  evaporated  per  pound  of  combustible  from  actual  temperature  and  pressure        4.05 

Water  evaporated  per  pound  of  bagasse  from  and  at  212°  F.          2.46     " 

Water  evaporated  per  pound  of  dry  bagasse  from  and  at2i2°F 4  •  41 

Water  evaporated  per  pound  of  combustible  from  and  at  212°  F 4-5° 

RATE    OF    COMBUSTION. 

Fuel  actually  burned  per  sq.  ft.  of  grate  surface  per  hour          70 .  2 

Dry  fuel  actually  burned  per  sq.  ft.  of  grate  surface  per  hour 39.1" 

Combustible  burned  per  sq.  ft.  of  grate  surface  per  hour 38.5 

Fuel  combustible  burned  per  sq.  ft.  of  heating  surface  per  hour 1.95     " 

Dry  fuel  burned  per  sq.  ft.  of  heating  surf  ace  per  hour 1.09     " 

Combustible  burned  per  sq.  ft.  of  heating  surface  per  hour 1.07      " 

RATE    OF    EVAPORATION. 

Water  evaporated  from  and  at  212°  F.  per  sq.  ft.  of  heating  surface  per  hour      .  4 . 80     " 

Water  evaporated  from  and  at  212°  F.  per  sq.  ft.  of  grate  surface  per  hour    .      .  I72-S     " 

Water  evaporated  from  100°  F.  and  70  Ibs.  gauge  pressure 144,121      " 

Water  evaporated  from  100°  F.  and  70  Ibs.  gauge  pressure  per  hour  .             .      .  24,020     " 

COMMERCIAL    HORSE-POWER. 
H.  P.  rated  at  30  pounds  water  per  hour  evaporation  from  100°  F.  and  70  Ibs 

gauge  pressure 800 

Builders  rating  in  horse-power 500 

Per  cent,  developed  above  rating 60 

Mr.  Pharr  referring  to  this  test,  said:  "The  results  will  probably  be  considered  extra 
good,  but  this  test  was  made  during  an  ordinary  run  and  no  precautions  were  taken  to 
obtain  favorable  results." 


150 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


labor  costs  to  a  minimum,  and  one  man  can 
operate  six  boilers,  where  ordinarily  five  or 
six  men  would  be  required. 

Success  of  the  Stirling  System — The 
extensive  application  of  the  improved  Burt 
furnace  is  evidenced  by  the  fact  that  about 
four-fifths  of  the  sugar  plantations  of  Louis- 
iana are  equipped  with  it,  and  in  almost 
every  case  in  connection  with  Stirling  boilers. 
The  Stirling  Company  has  installed  many 
bagasse-burning  outfits  in  the  West  Indies 
and  Hawaiian  Islands,  and  wherever  sugar 
cane  is  grown  Stirling  boilers  and  Burt 
Bagasse  Furnaces  are  the  combination  giving 
uniformly  satisfactory  results. 

Test  with  Bagasse  Fuel — The  preceding 
test  on  Stirling  boilers  burning  green  bagasse, 
made  by  Mr.  J.  N.  Pharr,  shows  an  evapora- 
tion probably  never  before  equaled  with  this 
fuel  in  this  country.  With  the  longer  lived 
tropical  bagasse  even  better  results  may  be 
obtained.  It  is  worthy  of  note  that  during 
the  test  the  boilers  were  working  at  sixty  per 
cent,  in  excess  of  their  rating. 

BURNING  PETROLEUM 

The  requirements  for  the  perfect  com- 
bustion of  petroleum  are: — it  must  be  thor- 
oughly atomized  and  mixed  with  the  requisite 
quantity  of  air;  the  mixture  must  be  burned 
in  a  furnace  constructed  of  refractory  material, 
which  will  be  durable  under  the  high  tem- 
perature developed,  and  radiate  heat  to  assist 
in  the  combustion;  and  the  combustion  must 
be  completed  before  the  gases  come  into 
contact  with  the  boiler  tubes. 

The  first  requirement  is  met  by  selection 
of  a  proper  burner.  The  other  requirements 
are  so  perfectly  met  in  the  Stirling  furnace 
that  the  changes  necessary  from  the  design 
for  coal  are  so  few  that'in  an  hour  after  shut- 
ting off  the  oil  burner  the  furnace  may  be 
made  ready  to  fire  with  coal. 

Fig.  32  shows  the  usual  arrangement  for 
oil  burning.  The  rear  half  of  the  grate  is 
covered  with  fire-brick  laid  close.  In  the 
front  half  of  the  furnace  the  bricks  are  laid 
with  air  spaces  between  them  varying  from 
l-m.  wide  directly  under  the  burner  tip,  to 
f-in.  wide  at  the  line  where  the  close  brick 
begins.  In  the  front  half  of  the  grate  those 
portions  not  directly  under  the  flame  are 


covered  with  fire  bricks  laid  about  ^-in.  apart, 
hence  the  wider  air  spaces  cover  an  area  of 
V  shape  under  the  flame.  A  space  f-in.  wide 
is  left  at  each  side  wall  to  admit  air  to  cool 
the  wall  and  promote  combustion. 

At  the  rear  of  the  grate,  or  on  the  bridge 
wall,  a  checkerwork  of  fire-brick,  from  14  to 
1 8  inches  high  is  usually  introduced  to  break 
up  the  heat,  and  prevent  it  from  striking 
directly  upon  the  tubes.  Owing  to  the 
recoil  of  the  gases,  and  necessity  for  ample 
space  in  which  they  can  expand,  the  fire 
arches  terminate  at  a  point  about  24  inches 
from  the  nearest  tube,  measured  at  right 
angles  to  the  tube.  The  spandrels  of  the 
arch  should  also  be  filled  level  so  as  to  leave 
a  throat  of  even  width  across  the  furnace. 
See  Fig.  59,  page  236. 

In  many  cases  the  grates  are  omitted,  and 
the  ash-pit  is  filled  with  ashes  or  refuse 
fire-brick,  up  to  a  line  connecting  the  top  of 
the  bridge  wall  and  bottom  of  the  ash-pit  door, 
and  this  arrangement  has  given  very  satis- 
factory results. 

When  the  grates  are  covered  with  fire- 
brick the  burner  is  introduced  through  either 
the  fire  door,  or  a  hole  in  the  pier  between 
doors ;  the  burner  tip  is  placed  about  6  inches 
above  the  fire-brick  over  the  grate,  and 
projects  the  flame  practically  parallel  with 
the  grate.  The  air  for  combustion  passes 
from  the  ash-pit  up  through  the  grates, 
absorbs  heat  in  its  passage  through  the  layer 
of  fire-brick,  mixes  with  the  atomized  oil, 
and  complete  combustion  ensues. 

When  the  grates  are  omitted  the  burner 
is  either  placed  as  before,  in  which  case  it 
is  directed  downward  slightly,  or  it  is  inserted 
on  a  level  with  top  of  ash-pit  doors. 

In  either  case  the  air  supply  is  regulated 
by  the  ash-pit  doors. 

Direction  of  the  Jet — If  the  proper 
quantity  of  air  is  supplied,  the  location  or 
direction  of  the  jet  has  no  influence  upon  the 
combustion,  but  it  has  considerable  influence 
on  the  efficient  utilization  of  the  heat.  The 
experiments  thus  far  made  indicate  that  the 
nearly  horizontal  jet  introduced  from  the 
boiler  front,  according  to  the  methods  above 
described,  gives  the  best  results.  As  soon 
as  the  heat  is  generated  it  is  essential  that 
it  be  absorbed  by  the  boiler  as  rapidly  as 
possible,  without  admixture  of  colder  gases 


STIRLING   BOILERS    FOR    BURNING   PETROLEUM 


151 


which  reduce  the  furnace  temperature.  In 
some  cases  burners  have  been  inserted  through 
an  opening  five  to  six  feet  above  the  floor 
line,  and  so  pointed  as  to  direct  the  flame 
downward;  it  then  crosses  the  grates,  reverses 


meets  the  gases  which  have  already  been 
cooled  by  contact  with  lower  part  of  the 
tubes,  and  the  mixture  of  the  two  causes 
a  reduction  in  temperature. 

Heating  the  Air  assists  in  the  combustion, 


direction  and  travels  up  the  front  bank  of     but   usually   the    complication    and    expense 


FIG.  32.      SECTIONAL   SIDE    ELEVATION    OF    STIRLING    BOILER    FOR    BURNING    PETROLEUM    OR    NATURAL  GAS 


tubes.  The  fire  arch  is  omitted.  Experi- 
ments show  that  the  efficiency  is  lowered  by 
this  arrangement,  because  it  exposes  a  larger 
wall  surface  to  the  intense  heat,  thus  causing 
greater  loss  by  radiation;  further,  that  part 
of  the  heat  which  rises  from  the  front  part 
of  the  flame  directly  to  the  top  of  the  furnace, 


of  doing  it  offset  the  advantage  when  steam 
spray  burners  are  used.  A  simple  and  com- 
paratively inexpensive  method  of  heating 
the  air  is  to  provide  the  boiler  with  hollow 
walls;  the  air  is  drawn  from  the  rear  of  the 
boiler,  absorbs  heat  from  the  inner  walls, 
and  is  admitted  through  ports  in  the  side 


152 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


walls,  both  above  and  below  the  grates. 
Installations  of  Stirling  boilers  thus  arranged 
have  proved  entirely  satisfactory. 

Whatever  arrangement  be  used  the  ad- 
vantages of  the  Stirling  furnace  as  described 
for  coal  apply  with  equal  force  to  oil. 


FIG    33      THE  WARREN  HYDROCARBON  BURNER 

Oil  Burners — The  function  of  the  burner 
is  to  pulverize  or  atomize  the  oil  to  a  con- 
dition approaching  as  far  as  possible  that 
of  gas,  thus  permitting  the  oil  to  be  burned 
like  a  gas  flame.  Of  the  many  hundred 
burners  invented  those  in  use  may  be  reduced 
to  two  classes;  (i)  Spray  burners,  in  which 
the  spray  is  made  by  a  jet  of  steam  or  com- 
pressed air;  (2)  Vapor  burners,  in  which  the 
oil  is  converted  into  vapor,  then  passed  into 
the  furnace. 

While  the  vapor  burner  possesses  merit,  it 
has  not  come  into  general  use.  In  spray 
burners  the  atomizing  agent  may  be  either 
steam,  compressed  air,  or  air  and  steam 
together.  The  steam  spray  burners  are 
almost  universally  used;  they  are  simple, 
require  no  blowers,  compressors  or  other 
apparatus  occupying  space  or  demanding 
attention,  and  in  the  better  types  now  ob- 
tainable at  reasonable  cost  the  steam  used 
is  so  little  as  to  be  of  less  value  than  the 
expense  of  saving  it. 


Spray  burners  of  the  older  types  usually 
consist  of  two  nozzles,  one  within  the  other; 
oil  is  fed  through  the  inner  and  steam  through 
the  outer  nozzle;  the  two  currents  meet  and 
mingle  and  atomization  is  then  effected. 
The  disadvantage  of  the  general  arrangement 
is  that  the  nozzles  occasionally  get  clogged 
by  dirt  or  formation  of  coke  due  to  the  heat, 
and  the  openings  wear  to  a  larger  size  than 
wanted.  Accordingly  the  later  types  of 
burner  dispense  with  the  arrangement  of  one 
nozzle  within  another. 

Steam  spray  burners  are  divisible  into  two 
classes:  (i)  Outside-mixers.  (2)  Inside- 
mixers.  In  the  former  the  oil  and  steam 
meet  outside  the  apparatus;  the  steam  flows 
out  through  a  flat  slit  or  through  a  series  of 
small  holes  in  a  horizontal  row;  the  oil  flows 
through  similar  slits  or  holes,  and  falls  into  the 
steam  which  seizes  and  atomizes  it.  Fig.  33 
represents  a  burner  of  this  type,  in  vented  by 
Mr.  James  W.  Warren,  of  Los  Angeles,  Cal. 
Its  construction  is  evident.  The  adjustment 
of  the  flame  is  easily  made  by  filing  the  tip  of 
the  central  washer,  and  wear  is  taken  up  by 
renewal  of  the  washer. 


FIG.  34.     HAMMEL  OIL  BURNER 

In  the  inside-mixers  the  oil  and  steam 
mingle  inside  the  apparatus  and  the  mixture 
is  atomized  by  passing  through  the  nozzle 
Fig.  34  represents  a  burner  of  this  type,  in- 
vented by  Mr.  Chas.  A.  Hammel,  of  Los 
Angeles,  Cal.  The  usual  inner  and  outer 
nozzles  are  eliminated,  and  wear  is  provided 


EFFICIENCIES   OBTAINABLE    FROM   OIL   FUEL 


153 


for  by  the  removable  plates  K-K.  The  oil 
passing  through  the  hole  D  is  atomized  by 
steam  jets  through  the  slots  G,  H,  and  /.  In 
burners  of  this  type  the  oil  requires  only 
sufficient  heating  to  enable  it  to  be  pumped 
through  the  oil  supply  system,  and  oils  or 
even  tar,  as  low  as  8°  Beaume  can  be  success- 
fully handled  owing  to  the  large  oil  channels. 

In  burners  of  the  outside-mixer  type  the  oil 
should  be  heated.  This  is  usually  done  by 
passing  the  oil  through  an  exhaust  steam 
heater.  The  action  of  the  burner  is  improved 
as  the  temperature  of  the  oil  is  increased,  up 
to  about  210  F.  If  raised  higher  the  water 
in  the  oil  will  vaporize  and  cause  the  flame  to 
sputter.  The  steam  supply  is  also  frequently 
superheated  by  passing  the  steam  pipe  either 
into  the  furnace  or  the  boiler  breeching. 
When  this  is  not  done  adequate  provision 
should  be  made  to  drain  out  entrained  water 
before  the  steam  reaches  the  burner.  A 
by-pass  between  steam  and  oil  supply  pipes 
should  be  provided  to  enable  the  oil  ducts  to 
be  occasionally  blown  out  with  steam.  See 
Figs.  33  and  34. 

Regulation  of  Oil  and  Steam  —  When 
starting,  the  oil  should  first  be  turned  on  and 
ignited  by  some  burning  waste;  then  the 
steam  should  be  turned  on ;  the  valves  con- 
trolling the  oil  and  steam  should  next  be 
regulated  so  as  to  get  the  proper  mixture. 
This  regulation  can  best  be  accomplished  by 
observing  the  top  of  the  smoke  stack,  and  the 
color  of  the  fire.  If  the  supply  of  steam  is  too 
great,  steam  will  be  seen  surrounding  the 
burning  spray  and  issuing  from  the  smoke 
stack;  if  the  steam  supply  is  deficient  the 
atomization  will  not  be  completed;  if  the  air 
supply  is  deficient  the  color  of  the  flame  will 
become  red,  and  smoke  will  issue  from  the 
stack,  indicating  incomplete  combustion. 
When  the  burner  valves  and  the  air  supply  are 
correctly  adjusted  the  flame  is  a  bright  white  in 
color  and  there  is  no  smoke.  Scintillating 
sparks  indicate  imperfect  atomization. 

Number  of  Burners  Required — This 
varies  with  the  type  of  burner.  With  either  of 
the  two  burners  already  described,  a  furnace  8 
feet  wide  can  be  served  by  one  burner,  a  fur- 
nace 14  to  1 6  feet  wide  by  three  burners  and 
intermediate  sizes  by  two  burners.  The 
essential  point  is  to  distribute  the  heat  evenly 
throughout  the  furnace,  and  evidently  the 


more  perfectly  the  burner  forms  a  wide  fan- 
tail  flame,  the  fewer  the  number  of  burners 
needed. 

Oil  Pressure — This  varies  from  a  few 
pounds  up  to  60  pounds  or  over  depending 
upon  the  type  of  burner.  The  oil  system  is  usu- 
ally fed  by  an  ordinary  duplex  steam  pump, 
with  a  relief  valve  between  the  suction  and 
discharge  sides.  This  is  set  at  the  desired 
pressure,  and  that  pressure  is  always  kept 
on  the  oil  line  to  insure  uniform  supply 
through  the  burner.  The  oil  passes  from  the 
pump  through  the  heater  then  to  the  burner. 
The  oil  system  should  be  provided  with  an 
air  chamber  to  neutralize  pulsations  of  the 
pump.  In  cold  weather  steam  is  circulated 
through  pipes  in  the  oil  tanks,  to  keep  the 
oil  in  condition  to  flow  freely. 

Per  Cent,  of  Steam  Used — In  a  series  of 
tests  made  by  the  Bureau  of  SteamEngineer- 
ing,U.  S.  Navy,*  it  was  found  that  with  a 
burner  using  air  as  an  atomizing  agent,  the 
amount  of  steam  required  to  compress  the 
air  varied  from  1.06  to  7.45%  of  the  total 
steam  generated,  the  mean  of  eight  tests 
being  3.18%.  Four  tests  on  steam  spray 
burners  varied  from  3. 98%  to  5.77%,  the 
average  being  4.8%.  Two  tests  on  burners 
using  steam  and  air  together  showed  8.54% 
and  6.09%  respectively.  In  a  series  of  most 
careful  tests  made  for  The  Stirling  Company 
on  latest  type  of  steam  spray  burner  the 
results  ran  from  2.10%  to  3.42%  averaging 
2.69%  for  four  tests.  It  therefore  does  not 
seem  that  any  saving  of  steam  is  to  be  made 
by  employing  air  as  the  atomizing  agent,  and 
the  use  of  steam  obviates  complication,  and 
risk  of  interrupted  service. 

Boiler  Efficiencies  obtainable  with  Oil 
Fuel — Since  oilcan  be  burned  with  admission 
of  but  little  more  than  the  amount  of  air  neces- 
sary to  furnish  the  actual  oxygen  necessary  for 
the  combustion,  and  the  furnace  doors  need 
never  be  opened  while  the  boiler  is  under 
steam,  and  the  boiler  heating  surf  ace  does  not 
get  quickly  fouled  by  soot,  it  follows  that  with 
proper  burners  and  careful  attention  higher 
boiler  efficiencies  may  be  expected  with  oil 
than  with  coal.  It  is  highly  important  to 
keep  down  the  content  of  water  in  the  oil. 
The  following  tests  on  the  Stirling  boiler 
indicate  the  efficiencies  obtainable  with  oil 
fuel.  It  should  be  noted  that  the  per  cent. 


*Report  of  the  Hohenstein  Boiler  and  Liquid  Fuel  Boards.     U.  S.  Government  Printing  Office,  1903. 


PART   OF  3.0OO   H.  P.  OF  STIRLING    BOILERS   BURNING   OIL,   THE   LOS   ANGELES   GAS   AND   ELECTRIC 

COMPANY'S  PLANTS,  LOS   ANGELES,  CAL. 


TEST    OF   STIRLING   BOILER   BURNING   OIL 


155 


of  water  in  the  oil  was  large,  hence  with  a 
smaller  content  of  water  even  higher  effi- 
ciencies would  have  been  developed,  illustrat- 
ing the  importance  of  sufficient  tankage  to 
allow  the  water  to  settle  out. 

Such  high  efficiencies  cannot,  however,  be 
obtained  with  boilers  that  are  not  particularly 
adapted  to  use  of  oil  fuel.  This  is  well 
shown  by  the  tests  made  by  U.  S.  Bureau  of 


BURNING  NATURAL  GAS. 

Practically  the  only  difference  between 
burning  petroleum  and  natural  gas  is  that 
ihe  former,  being  liquid,  must  be  atomized 
before  it  is  mixed  with  the  air  requisite  for 
combustion,  while  the  latter,  without  any 
change  of  state,  is  ready  to  be  mixed  with 
the  air  and  ignited.  Consequently  the  burners 


TESTS  OF   A  STIRLING  BOILER  OF  500  HORSE-POWER 

AT    PLANT    OF    THE    LOS   ANGELES    GAS    AND    ELECTRIC    COMPANY,    LOS    ANGELES,    CAL. 


2                  

.  *  .  square  feet, 

5,020 
Nov    i  ^ 

3y  gauge 
eed  water 
ation 

.  hours, 
....  Ibs. 
.  .  .  .  Fahr. 

7i 

120 

143° 

Ibs.  per  square  in. 

.      .      .      .    Fahr. 

Fahr. 


Name  of  boiler 

Heating  surface 

Date  of  test,  1902 

Duration  of  test 

Steam  pressure, 

Temperature  of 

Factor  of  evaporation 

Pressure  of  oil 

Temperature  of  oil 

Temperature  of  escaping  gases . 

Per  cent,  moisture  in  steam 

Total  water  apparently  evaporated Ibs. 

Total  water  evaporated  to  dry  steam Ibs. 

Equivalent  total  water  into  dry  steam,  from  and  at  2 1 2°  .  Ibs. 

Kind  of  burner  used 

Kind  of  oil  burned 

Per  cent,  of  water  in  the  oil 

Heat  value  of  oil  as  fired,  per  Ib B.  T.  U. 

Heat  value  of  oil,  freed  of  all  water        .      .      .      .     B.  T.  U. 

Total  oil  as  fired Ibs. 

Horse-power  developed 

Horse-power,  builders'  rating 

Per  cent,  developed  above  builders' rating 

Water  evaporated  from  and  at  21 2°  per  Ib.  of  oil  as  fired,  Ibs. 
Water  evaporated  from  and  at  212°  per  Ib.  of  oil  freed  of 

water Ibs. 

Efficiency  of  boiler 

Average  per  cent,  above  rating 

Average  efficiency  of  boiler 


24.7 

198 

5i8 

0-54 

117,960 


Warren 

Los  Angeles 

9.87 

17,122 

18,997 

9,i54 

523-9 

500        • 

4.78 


16 


15.81 
80.76 


53 
81.95 


Stirling. 
5,020 
Nov.  15 
5 


123 
I-I359 


o-54 
97,872 

97,343 
1  10,697 
Warren 
Los  Angeles 
9  .  16 
17,241 
18,979 
7,460 
641.4 
500 
28.28 


16,335 
83-14 


Steam  Engineering  already  referred  to.  There 
were  four  tests  at  rates  of  evaporation  per 
square  foot  of  heating  surface  equal  to  3.91 
5.18;  5.52;  and  5.82  pounds  of  water  from 
and  at  212°.  The  corresponding  boiler  effi- 
ciencies were  only  68.9;  71.5 ;  69.9,  and  66.7% 
The  boiler  was  of  the  water-tube  type  con- 
taining 2130  square  feet  of  heating  surface, 
and  operated  at  about  274  pounds  pressure. 


will  differ,  but  in  other  respects  the  form 
of  furnace,  length  of  fire-arches,  location  of 
the  checkerwork  wall  in  rear  of  the  furnace, 
location  and  height  of  the  burner  above  the 
fire-bricks  covering  the  grates,  and  the  air 
spaces  between  these  bricks,  will  be  the  same 
for  natural  gas  as  for  petroleum,  hence  the 
design  of  furnace  shown  in  Fig.  3 2  will  apply 
equally  well  to  both. 


NORTHERN    TEXAS    TRACTION    CO.,    HANDLEY,   TEXAS,    OPERATING    1,200    H.    P.    OF    STIRLING    BOILERS     BURNING    OIL 


TEST    OF    BOILER   BURNING    NATURAL   GAS 


157 


The  most  efficient  gas  burner  will  be  that 
one  which  most  intimately  mingles  the  gas 
and  air.  A  crude  form  of  burner  often  used 
consists  of  a  piece  of  one-half  inch  gas  pipe 
placed  inside  of  a  piece  of  2^-inch  pipe  which 
is  bricked  in  the  fire  door  opening.  The  suc- 


are  all  designed  for  the  purpose  of  effecting 
a  more  intimate  mixture  of  the  gas  and  air 
than  can  be  accomplished  by  the  simple 
arrangement  just  described.  The  quantity 
of  gas  fed  to  the  burner  is  regulated  by  an 
automatic  reducing  valve  which  is  controlled 


TEST  OF  A   STIRLING  BOILER  BURNING  NATURAL  GAS 

COLUMBUS,   BUCKEYE    LAKE,  AND  NEWARK  TRACTION   COMPANY,  HEBRON,  OHIO 

Duration  of  test,  hours 8 

Pressures:    .    .    Steam  gauge,  pounds 140 

Draft  in  rear  pass,  inches  of  water °-35 

Gas  at  meter,  ounces 8 

Temperatures:    Gas  at  meter 70°  F 

Feed  Water 116° 

Escaping  flue -gases 4*7° 

Kind  of  fuel Natural  Gas 

Cubic  feet  of  gas  consumed 103,900 

Cubic  feet  of  gas  consumed  at  32°  F.  and  14.7  Ibs.  absolute 99,183 

Total  water  used,  pounds 77,826 

Per  cent,  moisture  in  steam 0.65 

Total  water  evaporated  into  dry  steam,  pounds 77,320 

Factor  of  evaporation 1.1472 

Water  evaporated  into  dry  steam  from  and  at  212°,  pounds 88,700 

Water  evaporated  per  cu.  ft.  of  gas  at  standard  condition,  Ibs       ....  78 

and  from   and 

at  212.°  Ibs                                  895 

Horse-power  developed  during  the  test 321 

Horse-power,  builders'  rating 304 

Per  cent,  horse-power  developed  above  rating             .       .  5.6 


tion  created  by  the  gas  which  blows  out  under 
pressure  draws  through  the  annular  space 
between  the  two  pipes  a  portion  of  the  air 
needed  for  combustion,  and  the  additional 
air  required  passes  up  through  the  slots 
between  the  bricks  which  cover  the  grates. 
The  different  types  of  burners  on  the  market 


by  the  steam  pressure,  and  this  is  usually 
placed  in  the  pipe  which  supplies  gas  to  all 
or  a  number  of  the  boilers,  the  meter  being 
placed  between  reducing  valve  and  burners. 
The  above  test  indicates  the  high  effi- 
ciency obtainable  from  Stirling  boilers  fired 
with  Natural  Gas. 


The  Stirling  Chain  Grate  Stoker 


Chain  grate  stokers  are  extensively  used 
for  burning  lignites,  low  grades  of  bituminous 
coal,  and  small  sizes  of  anthracite.  One  of 
the  most  perfect  stokers  of  this  type  is  manu- 
factured by  The  Stirling  Company,  and  is 
illustrated  in  the  photograph  on  the  opposite 
page. 

The  stoker  consists  of  a  suitable  framework, 
a  travelling  grate;  fuel  hopper,  and  the  nec- 
essary driving  mechanism. 

The  stoker  is  entirely  self-contained,  and 
no  part  of  it  is  attached  in  anyway  to  the 
boiler  framework  or  the  brick  setting;  the 
entire  machine  rests  upon  four  wheels  which 
are  supported  by  suitable  rails  which  extend 
a  sufficient  distance  into  the  fire-room  to  enable 
the  stoker  to  be  drawn  completely  from  under 
the  boiler. 

The  framework  is  made  of  cast  iron  and  so 
designed  that  any  part  of  it  can  be  easily 
renewed.  In  the  rear  of  the  frame  is  a  shaft 
upon  which  are  placed  idler  pulleys,  and  a 
similar  shaft  in  front  is  equipped  with  sprocket 
wheels.  The  grate  is  an  endless  chain  com- 
posed of  links  of  narrow  width  and  relatively 
greater  depth;  this  chain  travels  over  the 
above  mentioned  pulleys  and  sprockets,  and 
is  driven  by  the  sprocket  shaft.  The  chain 
is  of  simple  construction  and  any  link  can 
be  replaced  without  disturbing  other  links. 
Between  the  front  sprocket  and  the  rear 
pulleys  the  chain  is  supported  by  cast  iron 
rollers  of  narrow  width,  strung  side  by  side 
on  shafts  extending  across  the  framework. 
Any  shaft  with  its  rollers  can  be  removed 
without  disturbing  any  other  part  of  the 
machine. 

To  provide  for  wear  and  expansion  of  the 
grate,  the  distance  between  centers  of  idler 
pulley  shaft  and  sprocket  shaft  can  be  quickly 
adjusted  even  while  the  stoker  is  in  operation. 
The  feed  gates  are  counterbalanced,  and  can 
be  quickly  adjusted  to  give  any  desirable 
thickness  of  fire.  Inspection  doors  placed 


in  the  side  of  the  furnace  permit  the  condi- 
tion of  the  fire  to  be  noted,  and  a  bar  to  be 
inserted  when  it  is  necessary  to  break  up 
clinkers  or  remove  obstructions  to  the  free 
passage  of  the  grates. 

A  common  defect  of  chain  grate  stokers 
is  the  admission  of  excess  air  from  the  ash 
tunnel.  In  the  Stirling  chain  grate  this 
defect  is  overcome  by  the  insertion  of  a 
diaphragm  between  the  stoker  and  the  ash- 
pit floor  at  a  point  just  in  front  of  the  ash-pit 
tunnel.  A  suitably  designed  opening  in  the 
diaphragm  permits  the  returning  portion  of 
the  grate  to  pass  through  without  admitting 
air,  hence  the  air  supply  must  come  into  the 
ash-pit  from  in  front  of  the  boiler,  where  it 
can  be  controlled  in  the  usual  manner. 

The  stoker  may  be  driven  from  any  con- 
venient source  of  power,  but  the  usual  method 
is  to  operate  it  from  an  overhead  shaft.  A 
connecting  rod  driven  from  this  shaft  operates 
a  crank  on  the  side  of  the  stoker  framework ; 
by  means  of  a  ratchet  this  crank  moves  a 
ratchet  gear  which  drives  the  sprocket  shaft 
through  the  medium  of  a  worm  wheel  and 
a  worm  shaft  attached  to  the  ratchet  gear. 
The  ratchet  may  be  adjusted  to  give  the 
grates  four  different  speeds,  as  occasion  de- 
mands. An  advantage  of  the  Stirling  chain 
grate  is  that  all  these  working  parts  are 
housed  in,  thereby  protecting  them  from 
dirt  and  grit.  The  connecting  rod  is  so^ 
designed  that  in  case  of  any  obstruction 
tending  to  impede  the  motion  of  the  grate,  the 
driving  mechanism  stops,  and  breakage  of 
parts  is  wholly  obviated. 

The  size  of  air  openings  in  the  links,  and 
other  minor  details,  depend  upon  the  character 
of  fuel  to  be  burned,  and  must  be  separately 
considered  in  each  case.  The  Stirling  Com- 
pany is  prepared  to  submit  designs  and  esti- 
mates for  chain  grate  stokers  adapted  to 
any  conditions  under  which  such  stokers  can 
be  advantageously  used. 


159 


ERECTING   300   H     P.   OF    STIRLING    BOILERS,   ILOILO    ELECTRIC    LIGHT    4    POWER    CO.,   ILOILO,   PHILIPPINE    ISLANDS 


160 


Utilization  of  Waste  Heat 


A  considerable  saving  of  fuel  and  labor  can 
be  made  by  utilizing  waste  heat  from  blast 
furnaces,  coke  ovens,  reverberatories  for 
smelting  ores,  etc.  While  this  fact  has  long 
been  known,  the  installation  of  equipment  for 
saving  waste  heat  has  not  become  so  common 
as  would  naturally  be  expected,  because  of 
the  lack  of  a  boiler  perfectly  adapted  to  the 
peculiar  nature  of  the  work  to  be  done. 
Boilers  of  the  shell  type  do  not  absorb  the 
heat  readily,  the  available  space  is  often  too 
small  to  permit  sufficient  capacity  of  such 
boilers  to  be  installed,  and  when  the  tem- 
peratures fluctuate  considerably  the  shell 
type  boiler  causes  trouble  from  unequal 
expansion.  The  requirements  as  to  space 
can  generally  be  met  by  installing  water-tube 
boilers,  but  not  all  boilers  of  that  type  can 
comply  with  the  other  requirements.  When- 
ever the  boiler  is  out  for  cleaning,  the  heat 
which  otherwise  would  be  utilized  by  the 
boiler  is  usually  wasted,  hence  it  is  essential 
that  the  boiler  can  be  cleaned  in  the  shortest 
possible  time.  The  character  of  the  gases 
also  may  vitally  affect  the  boiler  design.  For 
example,  the  gases  from  reverberatory  furnaces 
smelting  copper  matte  contain  a  large  con- 
tent of  sulphur,  hence  if  the  boiler  develops 
a  leak  sulphuric  acid  is  formed  and  the 
boiler  plate  is  quickly  destroyed.  The  sulphur 
fumes  will  penetrate  each  place  where  a 
leak  occurs,  therefore  in  those  boilers  using 
handhole  caps  the  bearing  surface  and  other 
parts  affected  by  leakage  from  the  caps  will 
soon  corrode,  which  explains  why  the  cap 
type  of  boiler  cannot  be  successfully  used 
in  connection  with  such  furnaces. 

These  disadvantages  are  so  completely 
obviated  in  the  Stirling  boiler  that  its  merit 
as  a  waste  heat  boiler  was  quickly  perceived, 
and  its  use  for  such  work  has  rapidly  in- 
creased. Not  only  has  it  met  all  require- 
ments in  a  most  satisfactory  manner,  but  it 
is  now  operating  with  gratifying  success  under 
conditions  of  service  which  no  other  boiler 
has  been  able  to  meet.  The  perfect  freedom 
from  expansion  obviates  straining  and  leaks; 
the  absence  of  caps  and  other  complication 
eliminates  the  necessity  of  stoppage  except 

*See  pages  20,  21  and  31. 


for  cleaning,  and  the  time  necessary  lor 
cleaning  is  less  than  required  by  other  types 
as  already  shown.*  The  manhole  plates  are 
the  only  parts  needing  removal,  and  they 
are  completely  outside  the  setting,  hence  are 
not  reached  or  affected  by  the  gases.  Large 
heating  surface  can  be  installed  in  the  small 
space  usually  available,  yet  in  no  case  need 
the  general  design  of  the  boiler  be  changed, 
and  should  occassion  demand  it,  the  boiler 
can  be  removed  and  reset  in  the  regular  way. 
The  form  of  furnace  can  be  modified  to  con- 
form to  the  requirements  of  the  particular  gas 
to  be  handled,  and  provision  be  made  for 
hand  firing  when  the  supply  of  waste  heat  is 
cut  off. 

Each  case  requires  careful  study  of  all 
the  conditions  in  order  to  determine  the 
best  method  of  utilizing  the  heat,  and  The 
Stirling  Company  will  be  pleased  to  confer 
with  prospective  customers,  and  to  submit 
designs  covering  their  requirements.  The 
following  descriptions  will,  however,  indicate 
in  a  general  way  the  amount  of  heat  which 
may  be  saved,  and  the  adaptation  of  the 
Stirling  boiler  to  this  class  of  service. 

Coke  Ovens — The  best  coking  coal  yields 
about  65  Ibs.  of  coke  per  100  Ibs.  of  coal. 
Assuming  the  heat  value  of  a  pound  of 
coke  to  be  13000  B.  T.  U.,  the  coke  produced 
by  one  pound  of  coal  will  represent  8450  B. 
T.  U.  The  heat  value  of  the  coal  would.be 
about  13500  B.  T.  U.,  hence  the  heat  loss 
during  the  coking  process  is  13500  -  8450  = 
5050  B.  T.  U.  Experience  has  shown  that 
about  one-half  of  this  is  lost  by  radiation  from 
the  oven  and  flue.  Of  the  remainder  about 
70%  can  be  utilized  by  a  proper  arrangement 
of  flues  and  stack  in  connection  with  a  boiler 
of  good  design  and  ample  heating  surface. 
Under  these  conditions  the  evaporation  per 
pound  of  coal  coked  will  be  about 

5050X0.5X0.70 

-—^—=1.83  pounds. 
965.8 

Assuming  that  one  oven  in  60  hours  will 
coke  6  tons  of  coal,  or  1,728,000  Ibs.  per  year, 
and  that  if  fired  under  the  boiler  direct  one 
pound  of  the  coal  would  evaporate  10  Ibs.  of 
water,  then  the  annual  saving  in  coal  per 


161 


162 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


oven  under  these  conditions  will  be 

1,728,000X1.83 

—  =158  tons. 
10X2000 

At  fifty  cents  per  ton  at  the  mine  this 
coal  represents  a  saving  of  $79.00  peryearper 
oven,  hence  allowing  20%  interest  and  depre- 
ciation, an  investment  of  $395.00  per  oven 


boiler.  The  stack  height  should  be  not  less 
than  125  feet,  or  higher  if  the  flues  are  long 
or  crooked.  The  flue  cross-section  should 
contain  .5  to  .75  square  feet  per  oven,  which 
limits  the  number  of  ovens  per  flue  to  about 
40.  Each  oven  contributes  enough  heat  to 
develop  10  to  12  boiler  horse-power. 


FIG.  35.     SECTIONAL  SIDE   ELEVATION 
OF  STIRLING   BOILER 


for   utilizing   the  waste  heat  would   be  war- 
ranted. 

The  arrangement  of  boilers,  flues,  etc.,  for 
a  waste  heat  installation  is  very  simple,  but 
the  details  require  close  attention.  The  gas 
flues  should  be  as  short  and  direct  as  possible, 
and  the  stack  must  produce  ample  draft  to 
draw  the  gases  through  the  flues  and  the 


WITH    UNDERGROUND    FLUE    FOR 
BURNING   COKE   OVEN   GASES 


The  foregoing  statement  applies  more 
particularly  to  the  bee-hive  type  of  oven. 
In  by-product  ovens  the  heat  loss  is  not  so 
large,  but  even  in  these  the  waste  heat  can 
be  utilized  at  a  handsome  profit. 

Heating  Surface  Required — When  the 
gases  reach  the  boiler  their  temperature  will 
not  exceed  2000°  and  may  be  less.  In  a 


BURNING  BLAST  FURNACE  GASES 


163 


boiler  fired  with  coal  the  furnace  temperature 
ranges  frojn  2500°  to  possibly  3000°,  hence 
the  heating  surface  per  boiler  horse-power 
should  be  greater  in  the  waste  heat  boiler 
than  in  the  direct-fired  boiler.  From  12  to 
1 5  square  feet  per  horse-power  will  be  needed 
for  water-tube,  and  from  15  to  20  feet  for 
return  tubular,  boilers.  Since  the  volume  of 
gas  is  large  and  its  temperature  comparatively 
low,  a  long  pass  through  which  the  gases 
travel  at  considerable  velocity  and  are  well 
broken  up  by  baffles,  is  of  marked  advantage 
in  utilizing  the  heat.  This  is  well  shown  by 
the  comparative  tests  on  Stirling  and  Lan- 
cashire boilers  as  later  given. 

Fig.  35  shows  the  Stirling  boiler  with  under- 
ground flue,  conveying  coke  oven  gases  to  the 
furnace.  The  gases  enter  through  an  opening 
which  extends  along  the  whole  length  of  the 
bridge  wall.  In  front  of  the  bridge  wall  is  a 
grate  for  firing  with  coal  when  the  gas  supply 
is  deficient,  but  it  is  better  practise  not  to 
fire  with  coal  when  the  boiler  is  utilizing 
waste  heat .  If  the  waste  gases  do  not  generate 
sufficient  steam,  an  additional  boiler  should 
be  installed  and  fired  exclusively  with  coal,  to 
attain  the  best  results. 

Tests — The  following  tests  indicate  the 
amount  of  heat  that  can  be  saved,  and  the 
advantage  of  the  Stirling  as  a  waste  heat 
boiler.  Owing  to  a  defective  damper  in 


the  gas  flue  leading  to  the  Stirling  boiler, 
the  leakage  into  the  by-pass  flue  was  sufficient 
to  produce  a  temperature  of  1440°  in  that 
flue.  If  the  heat  thus  lost  could  have  been 
passed  through  the  Stirling  boiler,  even 
better  results  would  have  been  obtained. 
These  tests  corroborate  the  statements  made 
that  the  heating  surface  for  best  efficiency 
with  waste  heat  boilers  should  be  greater 
than  for  coal-fired  boilers.  Under  ordinary 
circumstances  the  wate  -tube  boiler  will  work 
most  efficiently  at  a  rate  of  evaporation 
of  3.45  Ibs.  of  steam  from  and  at  212°  F.  per 
square  foot  of  heating  surface.  In  these 
tests  the  evaporation  on  the  Stirling  was  4.01 
Ibs.  per  square  foot;  if  this  had  been  reduced 
to  3  Ibs.  it  is  evident  that  the  temperature 
of  the  exit  gases  would  have  been  reduced, 
thus  increasing  the  efficiency. 

Blast  Furnace  Gases.. — Each  ton  of  iron 
produced  in  the  blast  furnace  requires  from 
i, 800  to  2,200  Ibs.  of  coke,  and  the  weight 
of  gases  produced  will  be  five  to  seven  times 
the  weight  of  coke  used.  From  25  to  30  per 
cent,  by  weight,  of  these  gases  will  be  carbon 
monoxide  (CO).  From  Table  47  page  133,  the 
calorific  value  of  carbon  monoxide  at  32°  F. 
and  at  atmospheric  pressure,  is  339  B.  T.  U. 
per  cubic  foot,  and  4,350  B.  T.  U.  per  pound. 
By  burning  these  gases  under  a  boiler  it  is 
possible  to  utilize  a  large  percent,  not  only 


TESTS   OF  ONE  STIRLING,  AND  TWO  28  FOOT  X  8  FOOT  LANCASHIRE 
BOILERS  BURNING  COKE  OVEN  GASES 


VICTORIA-GARESFIELD  COLLIERY,   ROWLAND'S  GILL,  NEWCASTLE-ON-TYNE, 

i  Stirling 

Boilers Class  A, 

Standard. 

22 
.     1,6 1 1  sq.  ft. 

73-4  "     " 
.     6,465  Ibs. 

-     3>8°°  " 
294  " 


Number  of  Beehive  coke  ovens 

Boiler  heating  surface 

Boiler  heating  surface  per  oven 

Water  evaporated  per  hour  from  and  at  212°  F 

Coal  coked  by  above  ovens  per  hour 

Water  evaporated  from  and  at  2 1 2°  F.  per  oven  per  hour  . 
Water  evaporated  from  and  at  2 1 2°  F.  per  Ib.  of  coal  coked 
Water  evaporated  from  and  at  212°  F.  per  sq.  ft.  of  heating 

surface     

Approximate  temperature  of  gas  at  point  of  entry  to  boiler     . 

Approximate  temperature  of  gas  leaving  boiler 

Normal  evaporation  of  boiler  if  coal  fired  in  the  ordinary  manner 
Percentage  evaporation  secured  to  a  normal  evaporation  of  boiler 

if  coal  fired 


4.01 

1,720°  F. 

650°  F. 

6,445  Ibs. 

100.3% 


ENGLAND 

2  Lancashire 

Type,  each 

28'  X  8' 

37 

1,796  sq.  ft. 
48.6     "  " 
8,503  Ibs. 

6,39i    ' 
230  " 

i-33  " 

4-79   " 
1,700°  F. 
750°  F. 
12,500  Ibs. 


68% 


164 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


of  the  heat  produced  by  burning  the  carbon 
dioxide  but  also  of  the  heat  stored  in  the 
other  gases  at  the  high  temperature  at  which 
they  enter  the  boiler  furnace. 

The    Stirling   boiler   has   in   a   most   satis- 
factory  manner  met   every  requirement   for 


ber  which  enables  the  gases  to  be  thoroughly 
mixed  with  air,  and  completely  burned. 
The  grates  can  be  used  to  assist  in  making 
steam  when  there  is  a  short  supply  of  gas, 
without  making  it  necessary  to  burn  an 
excessive  amount  of  coal  for  this  purpose. 


FIG.  36.     SECTIONAL   SIDE    ELEVATION    OF  STIRLING    BOILER   FOR   BURNING   BLAST   FURNACE   GAS 


burning  blast  furnace  gases.  Fig.  36  shows 
one  of  many  designs  adapted  to  such  work. 
The  boiler  is  coal-fired  from  the  front  in  the 
usual  manner,  and  the  gases  are  brought  into 
the  setting  at  a  point  directly  under  the 
incandescent  arch.  The  dropped  arch  at 
the  rear  of  the  furnace  provides  a  large  cham- 


The  setting  is  provided  with  cleaning  doors 
so  that  any  accumulation  of  dust  can  be 
readily  removed  without  shutting  down  the 
boiler.  By  means  of  a  cleaning  door  in  the 
side  of  the  setting  in  front  of  the  middle 
bank  of  tubes,  accumulations  of  lime, 
dust,  etc.,  either  on  or  between  the  tubes, 


TEST    OF    BOILER    BURNING    BLAST    FURNACE   GAS  165 

can  be   readily  blown  off.     There  is  also  an          The   following   report   of   a   test   made   on 

ample  number  of  explosion  doors,  so  that  Stirling  Boiler  using  blast  furnace  gases 
should  there  be  an  explosion  of  gas  in  the  or  fuel  will  prove  of  interest.  Attention 
furnace,  the  setting  would  be  immediately  is  directed  to  the  very  satisfactory  results 
relieved  of  strains  due  to  internal  pressure,  developed  during  the  test. 

TEST  OF  A  STIRLING   BOILER  AT   BRIER  HILL   FURNACE,   YOUNGSTOWN,  O. 

USING    BLAST    FURNACE    GAS    AND    COAL    AS    FUEL 

Date  of  test ......  April    18,  1899 

Duration  of  test,  hours 7:00 

Heating  surf  ace,  square  feet 2,788 

Grate  surface,  square  feet .' 52.64 

Pressures:    ....    Steam,  pounds  by  gauge        ...  80 

Barometer,  inches 28.67 

Gas  entering  furnace,  inches  of  water °-9I7 

Draft  at  flue  exit  over  damper,  inches  of  water      ...  0.45 

Draft  at  furnace,  inches  of  water 0.25 

Temperatures:    .    .    Gas  at  burners 322°  F 

Escaping  flue-gases 594° 

Feed  water 55° 

Outside  air .      .  98° 

Total  gas  used  at  burner  temperature,  cubic  feet 1,397,907 

"     "       "  32°  F                                                   881,965 

"     coal    "       pounds 245 

Heating  value  of  gas,  per  pound  at  32°     .      .      . B.  T.  U.  1,082.63 

"       "  cubic  foot  at  32°    .            B.  T.  U.  86.52 

"  coalused B.  T.  U.  12,592 

Total  water  used pounds  50,380 

Per  cent,  moisture  in  steam 0.6 

Water  evaporated  into  dry  steam pounds  50,078 

from  and  at  212° 60,745 

per  i, ooo  cu.  ft.  of  gas  at  32°.      .  54-57 
from  and  at  212°  per   1,000  cu.  ft. 

at  32° 66.19 

per   sq.    ft.    of   heating   surface   per 

hour 2.56 

from   and   at   212°   per  sq.   ft.   of 

heating  surface  per  hour    .      .  3  . 1 1 

Horse-power  developed         251.5 

Heat  delivered  to  boiler  per  hour  by  combustion  of    gas        .      .      .     B.  T.  U.  10,901,000 

coal       .      .      .  440,720 

gas  and  coal     .  11,341,720 

"  utilized  in  evaporation 8,382,948 

Efficiency  of  boiler percent.  73 .91 

Efficiency  of  boiler  not  including  hydrogen  in  heating  value  of  fuel  .        "     "    .  78.12 


Analysis  of  fuel-gas     %  BY  VOL.  %BYWT. 

CO2 I3-5°  20.00 

O o .  oo  o .  oo 

CO 25.20  23.62 

Hydrogen        .      .      .      .        1.43  0.097 

Nitrogen 59.87  56.25 

Specific  gravity 1-032 


Analysis  of  flue-gas.      %BY  VOL.     %BY  WT. 

CO2 14.00  20. 19 

O 9.20  9.59 

CO o 

Nitrogen  and  ) 
hydrocarbons  }      ' 


oo  o . oo 


76.80  70.2; 


Specific  gravity i .  0603 


400    H.   P.  OF  STIRLING    BOILERS   BURNING   GASES    FROM    PUDDLING    FURNACES. 
BLOCK-POLLACK    IRON   CO.,  CINCINNATI,  O. 


WASTE    HEAT    FROM    PLAIN    CYLINDER    BOILERS 


167 


Furnaces   for    Smelting    Copper — The 

gases  from  reverberatory  furnaces  smelting 
copper  matte  have  an  exit  temperature  which 
may  reach  or  even  exceed  2500°.  The  heat 
thus  carried  off  represents  a  large  per  cent,  of 
the  calorific  value  of  the  fuel  burned,  hence 
the  use  of  waste  heat  boilers  at  once  suggests 
itself.  The  problem  is,  however,  distinctly 
more  difficult  than  when  handling  coke  oven 
or  blast  furnace  gases,  because  of  the  presence 
of  a  large  content  of  sulphur  in  the  gases. 
If  these  gases  come  into  contact  with  water, 


as  a  waste  heat  boiler  in  connection  with 
furnaces  smelting  copper  matte. 

In  Puddling  and  Heating  Furnaces  the 

metal  to  be  heated  absorbs  only  a  small  per- 
centage of  the  calorific  value  of  the  fuel,  and 
the  remainder  passes  off  with  the  furnace 
gases.  A  considerable  portion  of  this  heat 
can  be  saved  by  a  properly  designed  waste 
heat  boiler.  The  saving  which  can  be 
effected  is  indicated  by  the  following  tests 
on  Stirling  boilers  installed  in  connection 
with  heating  furnaces. 


TABLE  50 

SUMMARY  OF  TESTS   OF  STIRLING  BOILERS  INSTALLED  IN 
CONNECTION  WITH  HEATING  FURNACES 


DATA 

OF    TESTS. 

AKRON 
IRON  CO. 

BLOCK-POLLACK 
IRON  CO. 

Heating  surface  square  feet 

1438 

I  ?I4 

Grate  surface  square  feet 

IQ  .  T.  C 

16.  < 

Ratio  heating  to  grate  surface 
Pounds  of  water  evap.  per  hou 

r         .             
from  and  at  212°  per  square  foot  of 
heating  surface     

74 
37.60 

3.06 

92. 

26.  12 
1.89 

from  and  at  212°  per  Ib.  of  coal 

7.09 

•9 

from  and  at  212°  per  Ib.  combustible 

8.48 

7-85 

sulphuric  acid  is  formed,  and  the  metal  of 
the  boiler  is  quickly  destroyed  by  corrosion. 
The  temperature  also  varies  considerably 
during  different  stages  of  the  smelting.  In 
consequence,  not  only  must  the  waste  heat 
boiler  be  so  designed  as  to  secure  perfect 
provision  for  expansion,  thus  obviating  leaks, 
but  it  must  also  be  free  from  handholes  or 
other  openings,  which  can  be  reached  by  the 
gases,  and  thereby  be  affected  by  the  corro- 
sion. The  Stirling  boiler  meets  these  require- 
ments perfectly.  The  curved  tubes  and 
suspended  mud  drum  provide  for  free  expan- 
sion and  contraction;  there  are  only  four 
openings — one  manhole  in  each  drum, — and 
these  are  all  outside  of  the  setting,  beyond  the 
reach  of  the  gases.  In  consequence,  the 
Stirling  boiler  is  perfectly  adapted  to  use 


Waste  Heat  from  Plain  Cylinder  Boil= 
ers. — Owing  to  the  deficient  heating  surface  of 
the  plain  cylinder  boiler,  the  breeching  tem- 
perature is  excessively  high  when  the  boilers 
are  forced.  In  consequence,  this  type  of 
boiler  is  now  fast  going  out  of  use,  but  where 
such  boilers  are  still  in  good  condition  it  has 
been  found  profitable  to  keep  them  in  service, 
and  utilize  the  heat  they  waste  by  passing  the 
gases  through  a  water- tube  boiler,  before 
turning  them  into  the  stack.  The  gases 
frequently  leave  the  cylinder  boilers  at  a 
temperature  of  1500°  to  1600°,  and  under 
such  conditions  the  waste  heat  absorbed  by 
the  water-tube  boiler  will  increase  the  capa- 
city of  the  plant  75  to  100  per  cent,  without 
burning  additional  coal,  or  increasing  the 
number  of  men  employed. 


Chimneys  and  Draft 


The  height  and  diameter  of  a  chimney 
depend  upon  the  kind  and  amount  of  the  fuel 
to  be  burned,  the  design  and  the  relative 
arrangement  of  the  boilers  and  flues,  and  the 
altitude  of  the  plant  above  sea  level.  Thus 
far  no  satisfactory  formula  involving  all 
these  factors  has  been  produced,  conse- 
quently empirical  methods  are  used.  In 
this  chapter  a  method  sufficiently  compre- 
hensive and  accurate  to  cover  all  practical 
cases  will  be  developed  and  illustrated. 

Draft  is  the  difference  in  pressure  which 
causes  gases  to  rise  in  a  stack.  If  the  air 
inside  a  stack  be  heated,  each  cubic  foot  of 
it  will  expand,  hence  its  weight  will  be  less 
than  that  of  a  cubic  foot  of  colder  air,  there- 
fore the  unit  pressure  at  the  stack  base  due 
to  the  column  of  heated  air  will  be  less  than 


that  due  to  a  column  of  cold  air  of  equal 
height.  This  difference  in  pressure,  like  the 
difference  in  head  of  water,  causes  a  flow  of 
cold  air  into  the  base  of  the  stack.  But  if 
in  its  passage  to  the  bottom  of  the  stack  the 
cold  air  has  to  pass  through  a  fire,  it  in  turn 
becomes  heated,  hence  it  also  will  rise,  and 
the  action  will  be  continuous. 

The  difference  in  pressure,  or  intensity  of 
draft,  is  usually  measured  in  inches  of  water. 

Assume  that  the  atmosphere  has  a  tem- 
perature of  62°  F.  and  the  temperature  of  the 
gases  in  the  chimney  is  500°  F.  Neglecting 
for  the  present  the  increased  density  of  the 
flue-gases  as  compared  to  air,  the  difference 
between  the  weight  of  the  external  air  and 
internal  flue-gases  per  cubic  foot  is  .034  Ibs., 
obtained  as  follows: 


TABLE  51 

THEORETICAL  DRAFT  PRESSURE  IN  INCHES  OF  WATER* 

IN  A  CHIMNEY  100  FEET  HIGH 
(For  other  heights  the  draft  varies  directly  as  the  height.) 


TEMP.  IN 
CHIMNEY 
FAHR. 

TEMPERATURE  OF  EXTERNAL  AIR.   (BAROMETER  30  INCHES.) 

0° 

10° 

20° 

30° 

40° 

50° 

60° 

70° 

80° 

90° 

100° 

200° 

•453 

.419 

.384 

•353 

.321 

.  292 

.263 

•234 

.  209 

.182 

•J57 

220 

.488 

•453 

.419 

.388 

•355 

.326 

.298 

.  269 

.244 

.217 

.  192 

240 

.520 

.488 

•451 

.421 

.388 

•359 

•33° 

.301 

.  276 

.250 

.225 

260 

•555 

.528 

.484 

•453 

.  420 

•392 

•363 

•334 

•309 

.282 

•257 

280 

•584 

•549 

•5*5 

.482 

•451 

.  422 

•394 

•365 

•340 

•3i3 

.288 

300 

.611 

•576 

•541 

•511 

.478 

•449 

.420 

•392 

•367 

•340 

•3i5 

320 

•637 

.603 

.568 

•538 

•5°5 

.476 

•447 

.419 

•394 

•367 

•342 

340 

.662 

.638 

•593 

•563 

•53° 

•501 

•472 

•443 

.419 

•392 

•367 

360 

.687 

•653 

.618 

.588 

•555 

.526 

•497 

.468 

•444 

.417 

•392 

380 

.710 

.676 

.  641 

.611 

•578 

•549 

.520 

.492 

.467 

.440 

•415 

400 

•732 

.697 

.662 

.632 

•598 

•570 

•541 

•5J3 

.488 

.  461 

•436 

420 

•753 

.718 

.684 

•653 

.  620 

•591 

•563. 

•534 

•5°9 

.482 

•457 

440 

•774 

•739 

•7°5 

.674 

.  641 

.612 

•584 

•555 

•53° 

•5°3 

•478 

460 

•793 

•758 

.724 

.694 

.660 

.632 

.603 

•574 

•549 

.522 

•497 

480 

.810 

.776 

.741 

.  7  10 

.678 

.649 

.  620 

•591 

.566 

•540 

•5*5 

500 

.829 

.791 

.  760 

•730 

.697 

.669 

•639 

.610 

.586 

•559 

•534 

*The  available  draft  will  be  the  tabular  values  less  the  amount  consumed  by  friction  in  the  stack.  In 
stacks  whose  diameter  is  determined  by  Formula  40  the  net  draft  will  be  80%  of  the  tabular  values.  Hence 
to  obtain  from  the  table  the  height  of  stack  necessary  to  produce  a  net  draft  of  say  0.6  inches,  the  the- 
oretical draft  will  be  0.6X1.25=0.75  inches,  which  can  be  got  with  a  stack  100  ft.  high  with  flue-gas 
temperature  of  420°  F.,  and  air  temperature  of  o°  F.,  or  a  stack  125  ft.  high  when  the  air  temperature  is  60°  F. 

169 


LOSS   OF    DRAFT    IN    STACKS 


171 


Weight  of  a  cubic  foot  of  air  at 

62°  F =.0761   Ibs. 

Weight  of  a  cubic  foot  of  air  at 

500°  F =.0414 

Difference      .      .     =.0347 

Therefore,  a  chimney  100  feet  high  would 
have  on  every  square  foot  of  its  base  cross- 
section  an  upward  pressure  of  .0347X100 
••  3.47  Ibs.  As  a  cubic  foot  of  water  at 
.62°  F.  weighs  62.32  Ibs.,  one  inch  of  water 
will  exert  a  pressure  of  ——•  =  5.193  Ibs. 
per  square  foot,  or  '"'^l3  =  0-03607  Ibs.  per 
square  inch.  The  100  feet  stack  will,  there- 
fore, show  a  draft  of  3.47  -s-  5.193  =  0.67  inch 
of  water,  nearly. 

For  the  determination  of  the  proportions 
of  stacks  and  flues  The  Stirling  Company's 
procedure  depends  upon  the  principle  that 
if  the  diameter  of  the  stack  is  sufficiently 
large  for  the  volume  of  gases  to  be  handled, 
the  intensity  of  draft  will  depend  upon  the 
height;  therefore, 

Select  a  height  of  stack  which  will  produce 
the  draft  required  by  the  character  and 
amount  of  fuel  to  be  burned  per  square  foot 
of  grate  surface,  then, 

Determine  for  this  stack  the  diameter 
necessary  to  handle  the  gases  without  undue 
frictional  losses. 

The  application  of  these  rules  follows. 

Draft  Formula — The  force  or  intensity  of 
draft  is  given  by  the  formula: 

D=o.  52  HXP !-----}  [36] 

*\* 

In  which, 

D=   draft    produced,    measured      in    inches 

of  water. 
H=  height    of     top    o"    stack    above    grate 

bars,  in  feet. 

P  =  atmospheric    pressure  in  Ibs.  per  sq.  in., 
T  =  atmospheric  temperature,  absolute. 
J\=  absolute    temperature  of  stack  gases. 

In  this  formula  account  is  not  taken  of 
the  density  of  the  flue-gases,  it  being  assumed 
to  be  practically  equivalent  to  that  of  air. 
The  error  is  safely  negligible  in  practise.* 
The  force  of  draft  at  the  sea  level — which 
corresponds  to  a  pressure  of  14.7  Ibs.  per 
square  inch — produced  by  a  chimney  100 
ft.  high,  when  the  temperature  of  the  at- 


mosphere  is  60°  F.,  and  the  flue-gas    tem- 
perature is  500°  F.,  is 


^=0.52X14.7     —          r=-67 
(  521       96i  ) 

Under  the  same  temperature  conditions 
this  chimney  at  a  pressure  of  10  Ibs.  per 
square  inch  —  which  corresponds  to  an  alti- 
tude of  about  10,000  feet  above  sea  level- 
would  produce  a  draft  of  only 

.0=0.52  X  ioo  X  10  (5^7-  <rlr)  =  °-45  inch. 

For  future  use  it  is  convenient  to  tabulate 
values  of  the  product. 


0.52X1.47--          -}-K 
(T       Tj 

for  a  number  of  different  values  of    7'x   and 
[36]   becomes 

D=KH  [37] 

For    an    atmospheric    pressure    and    tem- 

perature, respectively,  of  14.7  Ibs.  and  60° 

F.,  which  represent    average   conditions,  the 

results  are  as  follows: 


TEMPERATURE  OF 
STACK  GASES. 

75°  •    • 

70O  . 

650  .    . 

6OO  . 

550  •    • 
500  .    . 

45°  • 
400  . 

35°  •   • 


CONSTANT 
A' 

.0084 
.0081 
.0078 
.0075 
.0071 
.0067 
.0063 
.0058 
•0053 


Draft  Losses — The  force  of  the  draft  as 
determined  from  the  above  formula  can  never 
be  observed  with  the  draft  gauge  or  any 
recording  device,  but  if  the  ash-pit  doors  are 
closed  and  the  measurements  are  taken  at 
the  base  of  the  stack,  there  will  be  but  little 
difference  between  the  actual  and  the  theoreti- 
cal draft.  The  difference  existing  at  other 
times  represents  the  pressure  required  to 
force  the  gases  through  the  stack  against  the 
friction  of  the  sides  and  against  their  own 
inertia,  and  increases  witji  the  velocity  of  the 
gases.  When  the  ash-pit  doors  are  closed, 
the  volume  of  gases  passing  is  a  minimum, 
hence  the  maximum  force  of  draft  is  shown 
on  the  gauge. 

As  the  measurements  are  taken  farther 
along  the  path  of  the  gases  through  the  boiler, 


*Some  draft  formulas  are  based  upon  the  assumption  that  twenty-four  pounds  of  air  are  used  per  pound 
of  coal,  hence  the  air  will  weigh  96%  of  the  chimney  gas.  Table  51  gives  the  draft  pressures  in  inches 
of  water  worked  out  on  this  hypothesis.  Owing  to  the  variation  in  the  air  supply  the  draft  either  from 
the  table  or  from  Formula  [36]  will  be  accurate  enough  for  all  practical  purposes. 


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DIAMETER    OF  STACK    IN   INCHES 


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130 


FIG.  37.      CURVE   SHOWING    DIAMETER   OF  CHIMNEY   STACKS   AT   SEA   LEVEL 

COMPUTED  FROM  FORMULA  NO.  40.     FOR    BRICK   OR    BRICK-LINED  STACKS,   INCREASE  THE  DIAMETER  6  PER  CENT 
ONE-FIFTH    OF   THE    THEORETICAL   DRAFT    IS    LOST   IN    THE    STACKS 

172 


FORMULAS    FOR    DIAMETER    OF    CHIMNEYS 


173 


from  the  stack  toward  the  grate,  the  readings 
grow  gradually  less,  until  in  the  ash-pit  hardly 
a  perceptible  rise  takes  place  in  the  water 
of  the  gauge.  The  breeching,  the  boiler 
damper,  baffles  and  tubes,  and  the  coal  in 
the  grate,  all  retard  the  passage  of  the  gases, 
and  in  each  case  the  draft  from  the  chimney 
is  required  to  overcome  their  resistance. 
The  draft  at  the  rear  of  the  setting,  where 
the  connection  is  made  to  the  flue  or  stack, 
might  be  o.  5  inch,  while  in  the  furnace  over 
the  fire  it  might  not  be  more  than  0.15  inch, 
the  difference,  0.35  inch,  being  the  draft 
required  to  force  the  gases  between  the  tubes 
and  around  the  baffling. 

An  important  factor  in  chimney  design  is 
the  pressure  required  to  force  the  air  through 
the  bed  of  coals.  In  many  instances  this  will 
be  a  large  percentage  of  the  total  draft.  Its 
measure  is  found  directly,  in  the  case  of 
natural  draft,  by  noting  the  draft  in  the 
furnace,  for  it  is  evident  with  ash-pit  doors 
of  ample  size  the  pressure  under  the  grates 
will  not  differ  sensibly  from  the  atmospheric 
pressure. 

Loss  In  Stack — The  difference  between 
the  theoretical  draft  as  determined  by 
formula  [37]  and  the  amount  lost  by  friction, 
etc.,  in  the  stack  proper,  is  the  available  draft, 
or  that  which  the  draft  gauge  indicates  when 
connected  to  the  base  of  the  stack.  The  sum 
of  the  draft  lost  in  the  flue,  boiler,  and  furnace, 
must  be  exactly  equal  to  the  available  draft, 
and  as  these  quantities  can  be  determined 
from  records  of  experiments,  the  proportion- 
ing of  a  stack  resolves  itself  into  finding  a 
stack  which  will  produce  a  given  available 
draft. 

The  loss  in  the  stack  and  flue  by  friction 
and  inertia  can  be  calculated  from  the  fol- 
lowing formula: 

A0-2f*  [38] 

where  AD  =draft  lost  in  inches  of  water. 

W/=weight,   in     pounds,     of    gases 

passing  per  second. 
C  ==circumf  erence  of  a  stack  or  flue 

in  feet . 

^4=area  of  passage  in  square  feet. 
H  =height  of  stack  in  feet ;  or  when 

used  for  flues,   length  of  flue. 
/  =a    constant    with  the    following 

values,  for  sea  level: 


.0015  for  steel  stack,  temperature  of  gases  600°  F 
.0011  for  steel  stack,  temperature  of  gases  350°  F. 
.0020  for  brick  or  brick-lined  stack,  temperature  of 

gases  600°  F. 
.0015  for  brick  or  brick-lined  stack,  temperature  of 

gases  350°  F. 

The  available  draft  is  equal  to  the  difference 
between  the  theoretical  draft  from  Formula 
[37],  and  the  loss  from  Formula  [38],  hence 

fW2CH 


d'=  available  draft =K  H  - 


[39] 


Height  and  Diameter  of  Stack — It  fol- 
lows from  this  formula  that  a  stack  of  a 
certain  diameter,  by  increasing  its  height, 
can  be  made  to  produce  the  same  available 
draft  as  one  of  a  larger  diameter,  the  ad- 
ditional height  being  required  to  overcome 
the  greater  friction  loss.  Consequently, 
among  the  various  stacks  which  could  meet 
the  requirements  there  must  be  one  which 
can  be  constructed  cheaper  than  the  others. 
By  deducing  an  equation  connecting  the 
cost  of  stacks  with  their  height  and  diameter, 
and  using  it  in  connection  with  the  formula 
for  available  draft,  it  has  been  found  that 
the  minimum-cost  stack  has  -a  diameter  de- 
pending solely  upcn  the  horse-power  of  the 
boilers  it  serves,  and  a  height  proportional 
to  the  available  draft  required. 

Assuming  120  Ibs.  of  flue-gas  per  hour 
for  each  boiler  horse-power,  which  provides 
for  allowable  overload  and  use  of  poor  coal, 
the  method  above  stated  gives : 

For  an  unlined  steel    stack, 

Dia.  in  inches  =  4. 68  (H.P.f          [40] 
For    stacks    lined    with    masonry, 

Dia.  in  inches  =  4.92 (H.  P.y          [41] 

In  both  of  these  formulas  H.  P.  =  rated 
horse-power  of  boilers. 

From  this  formula  the  curve  in  Fig.  37  has 
been  calculated,  and  from  it  the  stack  di- 
ameter for  any  boiler  horse-power  can  be 
taken. 

Stacks  with  diameters  determined  as  above 
have  an  available  draft  which  bears  a  con- 
stant ratio  to  the  theoretical  draft,  and, 
allowing  for  the  cooling  of  the  gases  in  their 
passage  up  through  the  shaft,  this  ratio  is 
.80.  Using  this  correction  in  Formula  [37], 
and  transposing,  the  height  of  the  chimney 
becomes 


(U3J.VM  dO  S3HONI)    'Xld   HSV  QNV  POVNUOd   N33MX38   O3ain&3a 


dO  3OHOd 


DRAFT  REQUIRED  FOR  DIFFERENT  FUELS 


175 


H  = 


d' 
.8/C 


[42] 


H=  height  of  stack  in  feet,  measured  from 

the  point  where  the  flue  enters, 
d'  =  available  draft  required, 
K  =  constant  as  in  formula  [37]. 

Losses  in  Flues — The  loss  of  draftsuction 
in  passing  through  a  straight  flue  can  be 
calculated  approximately  from  Formula  [38], 
which  was  given  for  the  loss  in  a  stack. 
It  must  be  borne  in  mind  that  C  in  this 
formula  is  the  actual  perimeter  of  the 
flue,  and  is  least  compared  to  the  area  when 
the  section  is  a  circle,  is  greater  for  a  square, 
and  still  larger  for  a  rectangle.  The  re- 
tarding effect  of  the  square  flue  is  12%  greater 
than  of  a  circular  one  of  the  same  area. 
The  greater  resistance  of  the  more  or  less 
uneven  brick  flue  is  provided  for  in  the  values 
given  to  the  constants.  Both  steel  and 
brick  flues  should  be  short,  and  as  near  to  a 
circular  or  square  section  as  is  possible. 
Abrupt  turns  are  to  be  avoided,  but  long, 
easy  sweeps  take  up  valuable  space,  and  it  is 
often  desirable  to  add  to  the  height  of  a 
stack,  rather  than  take  up  additional  room 
below.  Short  right-angled  turns  reduce  the 
draft  by  an  amount  which  can  be  roughly 
approximated  as  equal  to  0.05  inch  for 
each  turn.  The  turns  which  the  gases  make 
in  leaving  the  damper  box  of  a  boiler  and 
entering  a  horizontal  flue,  must  always 
be  considered. 

The  sectional  area  of  the  passage  leading 
from  the  boilers  to  the  stack  is  determined 
largely  by  considerations  of  cost,  and  the 
subject  resolves  itself  into  whether  it  is 
cheaper  to  add  to  the  height  of  the  stack 
or  to  increase  the  flue  area.  The  general 
practise  is  to  make  the  area  of  the  flue  the 
same  as,  or  slightly  larger  than,  that  of  the 
stack ;  its  area  should  preferably  be  at  least 
20%  greater.  It  is  unnecessary  to  maintain 
the  same  size  of  flue  the  entire  distance 
behind  a  row  of  boilers,  and  the  area  may 
be  reduced  as  connections  with  the  various 
boilers  are  passed. 

With  circular  steel  flues  of  the  same  size 
as  the  stack  or  reduced  proportionately 
to  the  volume  of  the  gases,  a  convenient 
rule  is  to  allow  o .  i  inch  draft  loss  per 
each  hundred  feet  length  of  flue,  and 
0.05  inch  for  each  right-angle  turn.  For 


square  or  rectangular  brick  flues,  these 
values  should  be  doubled. 

Loss  in  Boiler — In  calculating  the  avail- 
able draft  of  a  chimney,  120  Ibs.  per  hour 
has  been  used  as  the  weight  of  the  gases  per 
boiler  horse-power.  This  covers  an  over- 
load of  the  boilers  to  an  extent  of  50%,, 
which  provides  for  all  practical  requirements, 
Stirling  boilers  require  comparatively  little 
draft  in  the  boiler  proper,  o .  2  inch  being 
all  that  is  lost  when  working  at  rated  ca- 
pacity. At  50%  overload,  0.4  inch  should 
be  allowed,  and  this  figure  is  the  one  to  be 
used  when  summing  up  the  available  draft 
the  stack  must  furnish. 

Loss  in  Furnace — The  draft  loss  in  the 
furnace  varies  between  wide  limits.  The 
air  necessary  for  combustion  must  come 
through  the  interstices  of  the  coal  on  the 
grate,  and  when  these  are  large,  as  with  a 
broken  lump  coal,  but  little  pressure  is  re- 
quired to  force  air  through;  but  if  they  are 
small,  as  with  slack  or  anthracite  culm,  a 
much  greater  pressure  is  required.  If  the 
draft  is  insufficient  the  coal  will  accumulate 
on  the  grate  and  a  dead,  smoky  fire  will 
result,  causing  imperfect  combustion;  if  the 
draft  is  too  great  the  coal  is  rapidly  con- 
sumed, leaving  a  thin  fire  and  portions  of 
the  grate  bars  uncovered. 

Draft  Required  for  Different  Fuels — 
For  every  kind  of  fuel  and  rate  of  combustion 
there  is  a  certain  draft  with  which  the  best 
general  results  are  obtained.  It  is  com- 
paratively small  with  the  free-burning 
bituminous  coal,  and  increases  in  amount  as 
the  percentage  of  volatile  matter  diminishes 
and  the  fixed  carbon  increases,  being  highest 
for  the  anthracites.  Other  things,  such 
as  the  percentage  of  ash  and  the  air  spaces 
in  the  grates,  etc.,  exert  an  influence,  but 
like  other  factors,  their  effect  can  be  found 
only  by  experiment. 

The  curves  in  Fig.  38  give  the  furnace 
draft  necessary  to  burn  various  kinds  of 
coal  at  the  combustion  rates  indicated  as 
abscissas.  These  have  been  plotted  from 
the  records  of  numerous  tests  in  the  files 
of  The  Stirling  Company,  and  they  allow 
a  safe  margin  for  economically  burning 
coals  of  the  kind  noted.  One  curve  is  given 
for  the  draft  required  with  Stirling  chain 
grates  burning  bituminous  slack.  The  greater 


176 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


draft  than  that  required  for  hand  firing  is 
due  to  the  fact  that  in  the  chain  grates  the 
fire  is  not  broken  up  and  cleaned.  As  the 
amount  of  fixed  carbon  in  coal  increases, 
the  differences  in  the  draft  required  by  a 
chain  grate  and  for  hand  firing  grow  less, 
and  for  culm  they  are  about  the  same ;  in  both, 
however,  the  draft  is  so  great  as  to  neces- 
sitate very  high  stacks  or  forced  draft. 

Rate  of  Combustion — The  amount  of 
coal  which  can  be  burned  per  hour  per 
square  foot  of  grate  is  controlled  by  the 
character  of  the  coal  and  the  ratio  of  grate 
surface  to  boiler  heating  surface.  When 
this  ratio  is  properly  proportioned  the 
efficiency  of  boiler  and  furnace  will  be 
practically  the  same  for  different  rates  of 
combustion  (unless  they  are  either  unduly 
large  or  small) ,  provided  the  draft  is  adjusted 
to  suit  the  particular  rate  of  combustion 
desired.  Hence  the  area  of  the  grate  can  be 
fixed  and  the  stack  be  designed  to  suit,  or 
the  stack  may  be  decided  upon,  and  the 
grate  area  be  adjusted  to  burn  the  necessary 
quantity  of  coal  at  a  rate  per  square  foot 
of  grate  corresponding  to  the  draft  the 
stack  can  provide. 

Solution  of  a  Problem — The  stack  di- 
ameter can  be  determined  from  the  curve, 
Fig.  37.  The  height  is  determined  by 
adding  the  draft  required  in  furnace,  boiler, 
and  flue,  and  computing  from  formula  [37] 
the  height  necessary  to  give  this  draft. 
Example:  proportion  a  stack  for  1000  H.  P. 
of  boilers,  using  chain  grates,  burning  fuel 
that  will  evaporate  8  pounds  of  water  from 
and  at  212°  per  pound  of  coal;  ratio  of 
heating  surface  to  grate  surface  being  40  to 
i;  the  flue  being  100  feet  long,  with  two 
right-angled  turns;  the  chimney  to  be  able 
to  handle  boiler  overloads  of  50%. 

The  atmospheric  temperature  may  be 
assumed  as  60°  F.,  and  the  flue-gas  tem- 
perature at  the  stated  boiler  overload  as 
550°  F. 

The    combustion    rate    at   boiler   rating   is 

40  X  si 

— - —  =  17-5  pounds. 

o 

For  50%  above  rating,  the  combustion 
rate  will  be  about  60%  more  than  this,  or 

1.60X17.5  =  28  Ibs.  of  coal  per  sq.  ft.  of 
grate  surface  per  hour.  The  furnace  draft  re- 
quired for  this  combustion  rate,  from  the 


curve,  Fig.  38,  is  0.4  inch.  The  loss  in  the 
boiler  also  will  be  0.4  inch,  the  loss  in  the 
flue  o.i  inch,  and  in  the  turns  2X0.05=0.1 
inch.  The  available  draft  required  at  the 
chimney  where  the  flue  enters  is  therefore: 


Boiler 

Furnace  . 

Flue  .  . 

Turns  . 

Total  . 


0.4  inch 
0.4 
o.i 
o.i     " 


i.o  inch 

Since  the  available  draft  is  80%  of  the 
theoretical,  the  theoretical  draft  due  to  the 
height  required  is  I.OOH-. 8  =  1.25  inch. 

The  chimney  constant  for  temperatures  of 
60°  and  550°  F.  is  .0071,  formula  [37],  hence 
the  height  of  the  stack  above  the  point  where 
the  flue  enters  is,  by  the  same  formula 


.  0071 

Its  diameter,  from  the  curve  in  Fig.  37, 
is  75  inches  if  unlined,  and  80  inches  inside 
if  lined  with  masonry.  The  greatest  diameter 
of  the  breeching,  if  circular,  for  20%  greater 
area  than  the  stack,  would  be  82  inches,  and 
would  taper  down  to  about  42  inches  where  the 
last  boiler  connects,  if  four  units  were  used. 

Correction  for  Altitude — From  formula 
[36]  it  follows  that  the  draft  is  proportional  to 
the  atmospheric  pressure,  hence  for  a  stack 
of  given  height  the  draft  will  decrease  when 
the  altitude  is  increased,  consequently  to 
secure  at  high  altitudes  the  draft  necessary 
for  the  rates  of  combustion  in  Fig.  38  the 
dimensions  of  a  stack  as  determined  for  sea 
level  must  be  altered. 

Let  p  be  the  atmospheric  pressure  at  sea 
level,  and  pv  the  pressure  at  any  other  alti- 
tude; H  the  height  of  a  chimney  which  at 
sea  level  produces  a  given  draft,  and H^, the 
height  of  a  stack  which  will  give  at  the  as- 
sumed altitude  the  same  draft  that  H  gives 

P 
at  sea  level.     Put  —=r,  then  from  formula 

ft 

[36],  H^=rH.  It  therefore  remains  only  to 
determine  the  increased  diameter  needed. 
Formula  [18],  page  87,  shows  that  the 
weight  of  gas  per  minute  flowing  through  a 
pipe  is 

r  pod*   i* 

w=a  constant  X  •<  ( 


SIZES    OF    CHIMNEYS    BY    KENT'S    FORMULA 


177 


Let  d=diameter  of  the  stack  H  deter- 
mined for  sea  level;  d^  the  diameter  of  H^ 
•determined  for  the  altitude;  D  the  density 
of  gases  at  sea  level,  and  Dt  the  density  at 
the  given  altitude.  In  the  formula  P  will 
•evidently  be  the  quantity  AD,  in  formula 
[38]  page  173,  which  will  be  the  same  in  both 
stacks  H  and  //,;  regardless  of  the  altitudes 
the  same  weight  of  oxygen  will  be  needed 
to  burn  a  pound  of  a  given  coal,  hence  the 
•diameter  of  stack  H 1  must  be  such  as  to  pass 
the  same  weight  of  gas  at  the  altitude  that 
stack  H  passes  at  sea  level.  To  apply  the 
formula,  H  and  //,  ,  will  be  the  lengths  de- 
noted by  L;  also,  as  previously  shown,  H^  = 
rH  and  D=rD^,  hence  since  both  stacks 
deliver  the  same  quantity  of  gas,  it  follows, 

!i!{ 

d' 


neglecting  the  small  term 


.that 


PDd5      PDjl*       D^rtf 
—  or 


H  Hl  H          rH 

Whence  dt**dr*,  hence  the  following  rule 
to  determine  stack  dimensions  for  any 
altitude:  Divide  the  barometric  pressure  at 
sea  level  (=30")  by  the  barometric  pressure 
at  the  given  altitude,  and  call  the  quotient  r. 
Determine  the  stack  height  and  diameter 
required  at  sea  level,  then  multiply  the 


height  so  determined  by  r,  and  the  diameter 
by  r%  and  the  resulting  dimensions  apply 
at  the  given  altitude.  The  flue  area  can  be 
determined  in  the  same  way. 

Table  52  gives  values  of  r  and  rl  com- 
puted from  data  in  Table  12.*  These  show 
that  altitude  affects  the  height  more  than 
the  area,  and  that  practically  no  increase 
of  area  is  needed  for  altitudes  up  to  3,000 
feet.  The  grate  areas  should  be  increased 
in  the  same  proportion  as  the  stack  areas 

TABLE  52 


Altitude 

Atmospheric 

9 

in  Feet  above 

Pressure. 

r 

rl 

Sea  Level. 

Lbs.per  Sq.In. 

5,221 

8.  19 

.80 

27 

4,075 

8.56 

.72 

24 

2,934 

8.94 

.65 

22 

1,799 

9-33 

•  ss 

20 

0,1  27 

9-95 

.48 

17 

9.031 

0.38 

•  42 

15 

7,932 

0.82 

.36 

13 

6,843 

i  .28 

.3° 

1  1 

5-764 

i  .  76 

•  25 

09 

5,225 

2  .01 

.  22 

08 

4,160 

2-51 

.18 

07 

3,115 

3-03 

-  13 

05 

2,063 

3-57 

.08 

03 

1,539 

3.84 

.06 

,  02 

Kent's  Table — Mr.  William  Kent  has 
prepared  a  table  giving  the  size  of  boiler 
chimneys  that  has  met  with  much  approval. 


TABLE  53 
DIMENSIONS    OF    CHIMNEYS    BY    KENT'S    FORMULA 


Diameter  in 
Inches. 

1 
t| 
1 

HEIOHT  OP  CHIMNEV  IN  KEET. 

200 

I 

hi. 

nil 

lg|| 

1  1 

Diameter  in 

Inches 

80 

86 

•0 

16 

too 

106 

110 

116 

120 

126 

ISO 

136 

140 

146   160 

165 

160 

166 

170 

176 

180 

186 

190 

196 

COMMERCIAL  HORSE  POWER 

30 

4.91 

107 

its 

110 





— 



E 













E 



17 

80 

3* 

S.U1 

1S7 

178 

— 











80 

88 

M 

7.0; 

Id 

196 

IKS 









— 



82 

88 

M 

8.80 

202 

20t> 

214 

—  

86 

m 

48 
48 

9.62 

li.67 

Ml 
111 

288 
820 

24* 

880 

261 

aim 

858 
S48 

286 
866 

871 

806 

878 

881 

888 

S'.Mi 





88 
48 

48 

48 

(4 

16.90 

~l9.64~ 

• 

416 

427 

488 
661 

44» 
686 

«»4 

481 

472 

482 

498 

608 
882 

618 
844 

628 

682 

642 

692 

849 

704 

"»«4 



— 





48 

64 
«0~ 

60 



M« 

67* 

6»« 

728 

HIM! 

81* 

667 

66» 

680 
886 

716 

877 

918 

64 

M 

88.76 

«78 

711 

744 

780 

776 

781 

806 

821 

8!)1 

904 
1  089 

1291 

6» 

88 

11 

78 

28.27 

8.1.  IS 







886 

868 
1014 

878 

1088 
1214 

*>(! 

1082 
1241 

818 
1084 

084 
1107 

862 
1128 

•70 

1160 
1846 

HUN 

1171 

100U 
1ID2 

1028 

1218 
1418 

1040 
12K2 

1068 
1262 

107S 
1272 

1106 
1810 

1120 

1828 
1668 

1186 

1846 
1674 

1161 

1864 
1696 

1882 

1400 
1«S7 

84 
70 

72 

78 

84~~ 

84 

(8.48 

1268 

1294 

1820 

1870 

1884 

1441 

1404 

1487 

1609 

1581 

1616 

76 

M 

44.18 



— 

1486 

1486 

1486 

1626 

1656 

1684 

1612 

l«Si> 

1BO« 

KllllI 

1719 

1746 

1771 

17M5 

1820 

1846 

1869 

1888 

80 

80 

8t 

511.27 

1848 

1678 

1718 

1747 

1780 

1818 

1846 

1876 

1907 
2166 

2481) 

1988 

196H 

1998 

2027 

205« 

2084 

2112 

2140 

2167 

88 

»« 

108 

108 

5B.75 
flil.llS 

1806 

1*44 

2100 

18H8 
22S4 

2021 
2276 

2068 
2818 

2084 
2869 

2180 
2899 

2200 

2478 

2284 
2516 

2268 
2654 

2:1111 
2592 

2888 
2628 

2888 

2664 
2982 
8816 

2897 
2700 

2429 
2786 

8469 
8771 

•1 

88 

lOt 

108 

114 

70.KN 









— 









24»9 

2647 

2694 

2886 

2640 
2988 

2686 

272» 

2778 
8084 

2816 

2868 

2900 

2941 

8022 

8081 
8406 

X100 

101 

114 

190 

7N.61 

2888 

2986 

8086 

8182 

8179 

8226 

8271 

8861 

8448 

107 

ito 

IN 

96.08 



8460 

8614 

8676 
4279 

8687 

S697 

8766 

8816 

8872 

8»29 

8984 

4089 

4098 

4147 

4200 

117 

182 

144 

111.10 

4206 

4862 

4424 

4496 

4666 

4682 

4701 

4768 

4884 

4899 

4988 

6026 

128 

144 

*See  page   58. 


178 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


For  ordinary  rates  of  combustion  of  bitu- 
minous coals  it  is  reliable,  provided  no 
unusual  conditions  are  encountered.  For 
ready  reference  in  cases  where  approximate 
dimensions  of  a  chimney  based  on  boiler 
horse-power  are  required  Mr.  Kent's  table 
is  extremely  convenient.  In  this  the  figures 
correspond  to  a  coal  consumption  of  5  Ibs. 
of  coal  per  H.  P.  per  hour.  Mr.  Kent  says: 
"This  liberal  allowance  is  made  to  cover 
the  contingencies  of  poor  coal  being  used, 
and  of  the  boilers  being  driven  beyond 
their  rated  capacity.  In  large  plants  with 
economical  boilers  and  engines,  good  fuel 
and  other  favorable  conditions,  which  will 
reduce  the  maximum  rate  of  coal  consump- 
tion at  any  one  time  to  less  than  5  Ibs.  per 
H.  P.  per  hour,  the  figures  in  the  table 
may  be  multiplied  by  the  ratio  of  5  to  tne 
maximum  expected  coal  consumption  per 
H.  P.  per  hour.  Thus,  with  conditions 
which  made  the  maximum  coal  consumption 
only  2 . 5  Ibs.  per  hour,  the  chimney  300  ft. 
high  X  12  ft.  diameter  should  be  sufficient 
for  6155X2  =  12,310  horse  power. 

STACKS  FOR  BOILERS  USING  OIL  FUEL 

The  requirements  for  stacks  attached  to 
boilers  burning  oil  are  entirely  different 
from  those  required  when  burning  coal. 
The  loss  of  draft  caused  by  a  bed  of  coals 
is  eliminated,  the  volume  of  flue-gas  will 
be  less  than  for  an  equal  weight  of  coal 
if  the  air  supply  is  properly  adjusted,  and 
the  action  of  the  burner  is  in  a  measure 
equivalent  to  a  forced  draft.  Experimental 
data  such  as  are  available  for  coal  have  not 
been  gathered  for  oil,  hence  no  such  elaborate 
methods  of  determining  proportions  of  stacks 
for  oil  as  have  been  worked  out  for  coal, 
are  at  present  available,  but  the  method 
to  be  given  has  been  found  entirely  satis- 
factory for  a  large  number  of  cases,  and 
may  be  used  without  hesitation. 

A  stack  75  to  80  feet  high  above  a  boiler 
damper  plate  furnishes  ample  draft  to  burn 
oil,  if  there  are  no  long  flues  or  turns  in  the 
breeching,  hence  the  only  other  requirement 
is  to  determine  the  diameter.  Owing  to 
the  smaller  volume  of  gas  formed  as  com- 
pared with  coal,  and  the  forced  draft  action 
of  the  burner,  it  has  been  found  by  ex- 


perience that  when  oil  is  burned,  a  stack 
having  60  per  cent,  of  the  cross  section  re- 
quired by  the  same  boiler  if  bituminous 
coal  were  used,  will  be  amply  large  to  enable 
the  boiler  to  be  fired  at  50  per  cent,  above 
rating  with  oil.  Example:  required  the 
dimensions  of  a  stack  for  500  H.  P.  of  boilers 
burning  oil.  500  X.  60  =  300.  Kent's  Table 
may  be  used  with  facility  in  this  case,  hence 
referring  to  this  it  will  be  found  that  a 
stack  48  inches  in  diameter  and  80  feet 
high  will  develop  311  H.  P.  with  bituminous 
coal,  hence  a  48-inch  stack  will  meet  the 
requirements  of  this  case.  Many  plants 
are  operating  successfully  with  stack  areas 
equal  to  only  50  per  cent,  of  the  coal  area,  but 
this  allowance  is  too  scant  to  provide  prop- 
erly for  overloads. 

Correction  for  Flues — It  has  already 
been  shown  that  a  flue  100  feet  long  loses 
o.i  inch  of  draft,  and  that  a  right-angled 
turn  loses  .05  inch.  But  Table  No.  51 
shows  that  for  a  stack  temperature  of  450° 
and  external  air  temperature  of  80°  the 
draft  in  a  loo-foot  stack  will  be  o.  549  inches, 
hence  the  draft  due  to  one  foot  of  height 
will  be  practically  0.0055  inches,  conse- 
quently for  each  elbow  in  the  breeching  an 
addition  of  10  feet  to  the  height  of  the 
stack  will  be  needed,  and  for  a  length  of  flue 
100  feet  long,  an  addition  of  o.i  -H  0.0055, 
=  18.1  feet,  will  be  sufficient. 

Where  local  conditions,  such  as  buildings, 
etc.,  necessitate  use  of  stacks  exceeding  80 
feet  in  height  the  corresponding  diameter 
may  be  found  in  the  same  way.  Example: 
if  for  1000  H.  P.  a  stack  140  feet  high  were 
assumed,  and  the  breeching  were  50  feet 
long  and  contained  two  right-angled  turns, 
the  part  of  the  height  required  to  give  the 
additional  draft  for  flue  and  turns  would 
be  2X10  +  9  =  29  feet.  140—29  =  111  feet. 
ioooX.6o=6oo  H.  P.  From  Table  53  a 
stack  60  inches  diameter,  and  no  feet  high, 
the  nearest  tabular  value  to  1 1 1 ,  is  equal  to 
593  H.  P.,  hence  a  6o-inch  stack  would 
be  suitable  for  the  given  conditions. 

DRAFT    GAUGES 

The  ordinary  form  of  draft  gauge  consist- 
ing of  the  U-tube,  Fig.  39,  containing  water, 
lacks  sensitiveness  when  used  for  measuring 


ELLISON'S    DRAFT    GAUGE 


179 


such  slight  pressure  differences  as  exist  in 
a  chimney,  hence  gauges  which  multiply  the 
draft  indications  are  more  convenient,  and 
are  much  used. 

Barrus5  Gauge — Mr.  G.  H.  Barms  for  a 
number  of  years  has  used  with  excellent 
results  an  instrument  which  multiplies  the 
ordinary  indications  as  many  times  as  is  de. 
sired.  It  is  illustrated  in  Fig.  40, and  consists 
of  a  U-tubemade  of  ^-inch  glass,  surmounted 
by  two  larger  tubes,  or  chambers,  each  having 
a  diameter  of  2^-inch.  Two  different  liquids 
which  will  not  mix,  and  which  are  of  differ- 
ent color,  are  used.  The  movement  of  the 
line  of  demarcation  is  proportional  to  the  dif- 
ference in  the  areas  of  the  chambers  and  of 
the  U-tube  connecting  them  below.  The 
liquids  generally  employed  are  alcohol  colored 


FIG.  39 
U-TUBE  DRAFT  GAUGE 


FIG.  40 
BARRUS'   DRAFT  GAUGE 


red  and  a  certain  grade  of  lubricating  oil.  A 
multiplication  varying  from  eight  to  ten  times 
is  obtained  under  these  circumstances;  in 
other  words,  with  ^-inch  draft  the  movement 
of  the  line  of  demarcation  is  some  2  inches. 


The  instrument  is  calibrated  by  referring  it 
to  the  ordinary  U-tube  gauge. 

Ellison's  Gauge — In  this  form  of  gauge 
the  lower  portion  of  the  ordinary  U-tube 
has  been  replaced  by  a  tube  slightly  inclined 
to  the  horizontal,  as  shown  in  Fig  41.  By 
this  arrangement  any  vertical  motion  in 
the  left  hand  upright  tube  causes  a  very  much 
greater  travel  of  the  liquid  in  the  inclined 
tube,  thus  permitting  extremely  small  va- 
riation in  the  draft  pressure  to  be  read  with 
facility. 


FIG.  41.     ELLISON'S   DRAFT  GAUGE 

The  gauge  is  first  leveled  by  means  of 
the  small  level  attached  to  it,  both  legs 
being  open  to  the  atmosphere.  The  liquid 
is  then  adjusted  (by  adding  to  or  taking 
from  it)  until  its  meniscus  rests  at  the  zero 
point  on  the  right.  The  left  hand  leg  is 
then  connected  to  the  source  of  draft  by 
means  of  a  piece  of  rubber  tubing.  Under 
these  circumstances,  a  rise  of  level  of  one  inch 
in  the  left  hand  vertical  tube  causes  the 
meniscus  in  the  inclined  tube  to  pass  from 
the  point  o  to  i.o.  The  scale  is  divided 
into  tenths  of  an  inch,  and  the  subdivisions 
are  hundredths  of  an  inch. 

The  right  hand  leg  of  the  instrument 
bears  two  marks.  By  filling  the  tube  to 
the  lower  of  these  the  range  of  the  instru- 
ment is  increased  one-half  inch,  i.  e.  it  will 
record  draft  pressures  from  o  to  i^  inches. 
Similarly,  by  filling  to  the  upper  mark,  the 
range  is  increased  to  2  inches.  When  so 
used  the  observed  readings  in  the  scale  are 
to  be  increased  by  one-half  or  one-inch, 
as  the  case  may  be. 

The  makers  recommend  the  use  of  a  non- 
drying  oil  for  the  liquid,  usually  a  300° 
test  refined  petroleum,  but  water  suffices 
for  all  practical  purposes. 


Analysis  of  Flue-Gases 


In  the  chapter  on  Combustion*  the  effect 
of  excess  air  in  cooling  the  fire  is  set 
forth.  This  excess  air  would  not  reduce  the 
boiler  efficiency  if  the  gases  of  combustion, 
when  sweeping  over  the  heating  surface, 
were  cooled  to  the  initial  temperature  of 
the  air  supply,  since  before  their  exit  they 
would  give  up  the  heat  they  absorbed  after 
entering  the  furnace.  Such  abstraction  of 
the  heat  is  not  possible  in  a  boiler  because 
the  flue-gases  cannot  be  reduced  to  a  tem- 
perature below  50°  to  100°  above  the  tem- 
perature of  the  steam.  With  a  fixed  tem- 
perature of  discharge  the  loss  in  the  waste 
gases  is  proportional  to  the  weight  of  the 
gases,  hence  excess  air  not  only  reduces  the 
temperature  of  the  furnace,  which  causes 
a  decrease  in  the  boiler  capacity  and  efficiency 
but  it  causes  still  further  loss  by  serving  as 
a  vehicle  to  convey  heat  to  the  stack. 

An  insufficient  air  supply  causes  formation 
of  carbon  monoxide  (CO)  instead  of  carbon 
dioxide  (CO2),  and  if  this  passes  away  un- 
burned  the  heat  derived  from  a  pound  of 
carbon  will  be  only  4450  B.  T.  U.  instead  of 
the  14600  B.  T.  U.  obtainable  when  carbon 
dioxide  is  formed. 

If  the  combustion  were  perfect  and  no 
excess  air  were  admitted,  the  resulting  gases 
would  be  carbon  dioxide,  and  steam,  to- 
gether with  the  nitrogen  from  the  air.  The 
amount  of  carbon  dioxide  and  nitrogen 
would  bear  a  fixed  ratio  to  the  carbon  burned. 
Consequently,  since  some  excess  air  is  un- 
avoidable, the  nitrogen  in  the  flue-gases  fur- 
nishes an  index  to  the  amount  of  that 
excess,  and  the  presence  of  carbon  dioxide 
indicates  incomplete  combustion  of  carbon. 

Object  of  the  Analysis — The  object  of 
the  flue-gas  analysis  is  to  determine  from  a 
sample  of  the  gas  the  amount  of  excess  air 
admitted,  the  degree  of  completeness  of  the 
combustion  of  the  carbon,  and  the  amount 
and  distribution  of  the  heat  losses  due  to 
the  excess  air  and  incomplete  combustion. 
The  quantities  actually  determined  by  the 
analysis  are  the  relative  proportions  of 
carbon  dioxide  (CO2),  carbon  monoxide 
(CO),  and  oxygen  (0)  in  the  gases.  Although 

*  Article  "Temperature  of  the  Fire,"  page  107. 


the  analysis  does  not  directly. determine  the 
amount  of  nitrogen  present  in  the  flue-gases, 
yet  its  actual  amount,  as  well  as  that  of  the 
air  supply,  may  readily  be  ascertained  by 
calculation.  When  air  is  drawn  through 
an  opening,  like  an  ash-pit  door,  sometimes 
an  anemometer  can  be  used  for  ascertain- 
ing the  velocity  through  the  area,  and  the 
air  supply  be  determined  by  these  means. 

Before  describing  in  detail  the  apparatus 
and  methods  used  for  analyzing  flue-gases, 
the  application  of  the  results  obtainable 
from  the  analysis  will  be  illustrated. 

A  pound  of  carbon  requires  for  complete 
combustion,  2.67  pounds  of  oxygen,  or  a 
volume  of  32  cubic  feet  at  60°  F.,  and  the 
gaseous  product,  carbon  dioxide  (CO2), 
when  cooled,  occupies  precisely  the  same 
volume  as  the  oxygen,  viz.,  32  cubic  feet. 
If  the  oxygen  is  mixed  with  nitrogen  in  the 
same  proportion  as  it  is  found  in  air  (20.91  O 
and  79.09  N),  the  volume  of  the  carbon 
dioxide  (CO2)  after  combustion,  and  also 
its  proportion  to  nitrogen,  is  the  same  as 
that  of  the  oxygen;  hence,  for  complete 
combustion  of  carbon,  with  no  excess  of  air, 
the  volumetric  analysis  of  the  flue  gases  is, 
Carbon  dioxide  .  .  CO2=2o.9i% 
Carbon  monoxide  .  CO  =None 
Oxygen  .  O  =None 

Nitrogen.  .  .  .  N  =79.09% 
If  the  supply  of  air  is  in  excess  of  that 
required  to  supply  the  oxygen  needed,  the 
combined  volumes  of  the  carbon  dioxide 
and  oxygen  are  still  the  same  as  that  of  the 
oxygen  before  combustion;  consequently, 
for  the  complete  combustion  of  pure  carbon, 
the  sum  of  the  percentages  by  volume  of  the 
carbon  dioxide  and  oxygen  in  the  flue  gases 
must  always  be  20.91,  no  matter  what  the 
slip  ply  of  air  may  be. 

Carbon  monoxide  (CO)  produced  by  im- 
perfect combustion  of  carbon,  occupies  twicQ 
the  volume  of  the  oxygen  entering  into  its 
composition,  and  renders  the  volume  of  the 
flue  gases  greater  than  that  of  the.  air  supply 
in  the  proportion  of 

hence 


i oo- i  the  %  of  CO' 


182 


THE    STIRLING    WATER-TUBE    SAFETY   BOILER 


when  pure  carbon  is  the  fuel,  the  sum  of  the 
percentages  of  carbon  dioxide,  oxygen,  and 
one-half  the  carbon  monoxide ,  must  be  in  the 
same  ratio  to  the  nitrogen  as  is  oxygen  in  air, 
i.  e.,  20. 91  to  79  .09 

The  action  of  hydrogen  in  coal  is  to  increase 
the  apparent  percentage  of  nitrogen  in  the  flue- 
gases,  because  the  water  vapor  condenses 
at  the  temperature  at  which  the  analysis 
is  made,  and  account  of  it  is  lost,  but  the 
nitrogen  that  accompanied  the  oxygen  with 
which  the  hydrogen  combined,  maintains 
its  gaseous  form  and  passes  into  the  analyz- 
ing apparatus  with  the  other  gases. 

Example — Suppose  an  analysis  of  flue- 
gases  shows  12.5%  of  carbon  dioxide,  0.6% 
of  carbon  monoxide  and  6.5%  of  oxygen, 
all  by  volume.  Then  nitrogen,  which  is  the 
only  other  constituent  in  the  flue-gases 
worthy  of  consideration,  will  represent  a 
percentage  of  the  total  volume, 

ioo-(i2.5+o.6+6.5)=8o.4% 
Assume  the  unit  of  volume  here  designated 
as  100%  to  represent  100  cubic  feet.      From 
Table    54,  the  weights  of  the  various  gases 
per  cubic  foot  are  as  follows: 

Carbon  dioxide  (CO2)  =0.12 2681 
Carbon  monoxide  (CO)  =0.078071 
Oxygen  (O)  -0.088843 

Nitrogen  (N)     =0.078314 

The  weight  of  the  flue-gas  per  unit  volume 
of  100  cubic  feet  will  therefore  be 


Carbon  dioxide       (CO2)  =  .12268X12.5  =  1.5534^3. 
Carbon  monoxide  (CO)     =. 07807  X   0.6=    .0468 
Oxygen         .      .      (O)        =  .o8884X    6.5=    .5775 
Nitrogen      .      .      (N)       =  .07831 X  80.4=6. 2961 

i  oo.o     8. 4738  Ibs. 

From  the  atomic  or  combining  weights 
of  the  elements,  it  is  known  that  in  a  unit 
of  carbon  dioxide,  oxygen  constitutes  eight- 
elevenths  of  the  weight,  the  remaining 
three-elevenths  being  carbon ;  and  in  carbon 
monoxide  four-sevenths  is  oxygen  by  weight, 
and  three-sevenths  carbon.  Therefore,  the 
weight  of  oxygen  in  100  cubic  feet  of  flue- 
gas  in  question  is. 

Oxygen  in   COa  .      .      =  1.5534X8/11  =  1.1297^3. 

Oxygen  in    CO  .      .      =0.0468X4/7   =0.0267 

Free  Oxygen  =        ...      =0.5775 

Total  weight  of  Oxygen     .      .      .      =1.7339  Ibs. 

The  weight  of  carbon  as  determined  from 
the  same  gas  analysis  is, 

Carbon  in  CO2      .      .      =  1.5534X3/11=0.4236^5. 
Carbon  in  CO        ...."". 0468 X  3/7   =0.0201 
Total  weight  of  Carbon      .      .      .       =0.4437  Ibs. 

As  atmospheric  air  supplied  to  the  fire 
contains  23.15%  of  oxygen  by  weight,  then 
the  weight  of  air  which  contained  1.7339 

i .  7339X100 
Ibs.  of  oxygen  is =7.49^5;  and, 

O   '        D 

as  this  amount  of  air  was  required  for  the 

combustion      of    0.4437      Ibs.      of      carbon, 

the   weight   of   air  per  pound  of  carbon  is 

7-49 


=  16.88  Ibs. 


0.4437 


TABLE  54 
DENSITY  OF  GASES  AT  ATMOSPHERIC  PRESSURE 

(Adapted  from  Kent.*) 


Relative  Density, 

Weight  of  One 

Cubic  Feet 

Hydrogen  =  i 

GAS. 

SYMBOL. 

Specific  Gravity 
Air=i. 

Cubic  Foot 
at  32°  F. 

per  Pound 
at  32°  F. 

Exact 
Relative 

Approximate 
Whole 

Densities 

Numbers. 

Oxygen. 

O 

I  .  10521 

0.088843 

11.257 

15.96 

16 

Nitrogen 

N 

o  .  9701 

0.078314 

12  .  764 

14.01 

14 

Hydrogen    .      .      . 

H 

0.069234 

0.005589 

178.930 

I  .  OO 

i 

Carbon  dioxide 

CO2 

1.51968 

o  .  122681 

8.158 

21-95 

22 

Carbon  monoxide 

CO 

o  .  96709 

0.078071 

12.818 

13-97 

14 

Methane 

CH4 

0-55297 

o  .  044640 

22.412 

7-99 

8 

Ethylene     . 

C,H, 

0.96744 

0.078100 

12  .  804 

13-97 

14 

Acetylene    . 

C2H2 

0.89820 

O.O73OIO 

I3-697 

12.97 

13 

Sulphur  dioxide 

S02 

2  .  21295 

o.  178646 

5-598 

31.96 

32 

Air 

I  .  OOOO 

0.080728 

12.383 

*Steam  Boiler  Economy,  p.  20. 


HEAT  LOST  IN  CARBON  MONOXIDE 


183 


If  the  coal  in  the  example  considered  con- 
tained 86%  of  carbon,  4%  of  hydrogen,  and 
2-5%  °f  °xygen>  then  the  air  per  pound 
of  coal=i6.88X- 86=14. 52  Ibs.,  disregarding 
the  hydrogen  and  oxygen.  But  the  oxygen 
in  fuel  renders  inert  ^  of  its  weight  of  hy- 
drogen, and  only  the  remainder  of  the  hydro- 
gen is  available  for  combustion;  therefore 
the  air  required  to  burn  the  hydrogen  is 

(  . 025  ) 

]  .04 —  ^34.56=.o369X34-56*=I-275  Ibs. 

f  8     ) 

Thus  the  total  air  supply  per  pound  of  fuel 
becomes  14.52+1.28=15.80  Ibs. 

Air  Required  and  Supplied — When  the 
ultimate  analysis  of  a  fuel  is  known  the  air 
required  for  complete  combustion,  with  no 
excess,  can  be  found  as  shown  in  chapter  on 
Combustiont  or  from  the  following  approx- 
imate formula: 

Pounds  of  air  required  per  pound  of  fuel= 


[43] 


34. 56  •? 

3 


where  C,  H  and  O=per  cent,  by  weight  of 
carbon,  hydrogen  and  oxygen  in  the  fuel, 
divided  by  100. 

When  the  flue-gas  analysis  is  known,  the 
total  amount  of  air  supplied  is,J 

Pounds  of  air  supplied  per  pound  of    fuel= 

3.032^  --  —  —  bet  [44] 

(C02+C0\ 

where  N,  CO  and  C02=percentage  by  vol- 
ume of  nitrogen  ,  carbon  monoxide  and  carbon 
dioxide  in  the  flue-gases,  and  C  the  propor- 
tionate part,  by  weight,  of  carbon  in  the  fuel. 
The  weight  of  the  flue-gases  will  be  one 
minus  the  per  cent,  of  ash  (expressed  in 
hundredths)  more  than  this,  i.  e.,  it  will  be 
the  sum  of  the  weights  of  the  air,  and  the 
combustible  and  moisture  in  the  fuel,  hence 
Weight  of  flue-gases  per  Ib.  of  fnel= 


3.032 


CO2  +  CO 
where    A=proportionate 
of  ash  in  the  fuel. 


-A)  [46] 

part,    by    weight, 


The  ratio  of  the  air  actually  supplied  per 
pound  of  carbon  to  that  theoretically  re- 
quired to  burn  it  is 

N 


3-032 


co9+co 


11.52 


=o. 2632 


C0 


[47] 


in  which  N,  C02  and  CO  are  the  percentages 
by  volume  in  the  flue-gas. 

The  ratio   of  the   air  supplied  per  pound 
of  fuel  to  the  amount  theoretically  required  is 

N 
N-3.7820 

which  is  derived  as  follows:  The  N  in  the 
flue-gas  is  the  content  of  nitrogen  in  the 
whole  amount  of  air  furnished.  The  oxygen 
in  the  flue-gas  is  due  to  the  air  supplied 
and  not  used.  This  oxygen  was  accom- 
panied by  3.782  times  its  volume  of  nitrogen. 
(AT- 3  .  782  0)  represents  the  nitrogen  content 
in  the  air  actually  required  for  combustion. 
Hence  N+  (N  —  3 . 782  0)  is  the  ratio  of 
the  air  supplied  to  that  required .  The  per  cent . 
of  excess  air  is  this  ratio  minus  one.  Table 
55  gives  the  values  of  this  ratio  correspond- 
ing to  various  percentages  of  CO2  +  CO  and 
CO2+CO  +  O 

The  heat  lost  in  the  flue-gases  is 

L,  =  o .  2 4  W (T  —  t)  [49] 

where 

L    =  B.  T.  U.  lost  per  pound  of  fuel. 
W  =  Weight     of    flue-gases    in    pounds    per 

pound  of  fuel. 

T   =  Temperature  of  flue-gases. 
t     =  Temperature  of  atmosphere. 
0.24  is  the  specific  heat  of  flue-gas. 

The   heat  lost  in  the   carbon  monoxide  in 
B.  T.  U.  per  pound  of  fuel  is 

CO 


where,  as  before,  CO  and  C02  are  the  per  cent, 
by  volume  in  the  flue-gas,  and  C  the  pro- 
portion (by  weight)  of  carbon  in  the  fuel. 


*Weight  of  air  required  for  the  combustion  of  one  pound  of  hydrogen,    t  Article,  "Air  Required,"  p.  106. 
JThe  derivation  of  this  formula  may  be  found  in  Kent's  Steam  Boiler  Economy,  First  Edition,  page  32. 
As  a  check  the  following  formula  may  be  used: 

Pounds  of  air  supplied  per  pound  of  fuel  =  n.52x  — p'U    ,nr\ —  XC  +  34-S6H1  [45] 

Where  H1  is  the  available  hydrogen  (H  -|O)  in  the  fuel.  This  formula  and  that  above  given  will  not 
produce  the  same  result  unless  the  flue-gas  and  coal  analyses  are  accurate,  and  the  sample  of  the  gas  is 
a  true  one.  The  more  accurate  the  work  the  more  nearly  the  formulas  will  agree. 


184 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


Orsat  Apparatus — The  analysis  of  the 
flue-gases  is  best  made  for  practical  pur- 
poses by  means  of  the  Orsat  apparatus, 
shown  in  Fig.  42.  The  operation  is  as 
follows:  Exactly  100  cc  of  the  gas  sample 
are  drawn  into  the  graduated  measuring 
burette,  A,  and  then  passed  in  succession 


tubes  placed  in  the  vessels  for  that  purpose, 
and  comes  in  intimate  contact  with  the  gas. 
Each  vessel  absorbs  a  different  constituent. 
D  is  filled  with  a  solution  of  potassium  hy- 
droxide and  takes  up  the  carbon  dioxide; 
E  contains  pyrogallic  acid,*  which  re- 
moves the  oxygen ;  and  F  absorbs  the  carbon 


TABLE  55 

RATIO    OF    TOTAL    AIR   SUPPLIED    TO   THAT   THEORETICALLY    REQUIRED 
FOR    VARIOUS    ANALYSES    OF    FLUE-GASES 


N 


N— 3.782  O 


CO2+CO 

N  =  79 
CO2+CO+O 

=  21 

N  =  7Q.5 
CO2+CO+O 

=  20.5 

N  =  8o 
CO2+CO  +  O 

=  20 

N  =  8o.s 
CO2+CO+O 
=  19-5 

N=8r 
CO2+CO  +  O 
=  IP 

N=8i.S 

CO2+CO  +  O 
=  18.5 

N=82 
CO2+CO+O 
=  18 

21 

I  .  OO 

20 

i.  <>S 

1  .02 

1  .00 

19 

I  .  II 

1.  08 

J-05 

1  .  02 

1  .00 

18 

1.17 

1.14 

I  .  10 

1.  08 

I-°5 

I  .02 

1  .00 

17 

1.24 

I  .  20 

1.17 

1-13 

I  .  IO 

1.07 

J-°5 

16 

1.32 

1.27 

1.23 

I  .  20 

i  .  16 

*-I3 

I  .  IO 

15 

I  .  40 

i-35 

I  31 

1.27 

1.23 

I  .  19 

1.16 

14 

*"-5i 

i-45 

i-39 

J-35 

1.30 

I  .  26 

1.23 

13 

1  .62 

i-55 

J-S0 

1.44 

i-39 

!-34 

1.30 

12 

1.76 

1.68 

1.61 

1-54 

i  .49 

J-43 

1.38 

II 

1  .92 

1.82 

i-74 

1.66 

i  .60 

i-53 

1.48 

IO 

2  .  I  I 

2    OO 

i  .90 

1.81 

1.73 

1.65 

i-59 

9 

2.35 

2.21 

2.08 

1.97 

1.88 

i-79 

1.71 

8 

2.65 

2.47 

2.31 

2.18 

2  .06 

1.  95 

1.86 

7 

3-°3 

2.80 

2.59 

2.44 

2  .  27 

2.14 

2.03 

6 

3-55 

3-22 

2  .96 

2.74 

2-54 

2     38 

2  .  24 

5 

4.27 

3.81 

3-44 

3-J4 

2.89 

2.68 

2.50 

4 

5-37 

4-65 

4.11 

3.68 

3-34 

3-°5 

2.83 

3 

7-23 

5-97 

5-Jo 

4-45 

3-96 

3-56 

3-25 

2 

ii  .06 

8-34 

6.71 

5-63 

4.85 

4.27 

3.82 

I 

23-51 

13-83 

9-83 

7.64 

6  .  27 

6.12 

4.64 

into  the  U-form  absorbing  vessels,  D,  E,  F, 
each  time  being  returned  to  and  measured 
in  A.  In  passing  into  the  U-shaped  vessels, 
the  gas  displaces  the  liquid  contained  therein , 
driving  it  up  into  the  other  legs.  A  portion 
of  the  fluids,  however,  adheres  to  the  glass 


monoxide  in  a  solution  of  cuprous  chloride. 
The  reduction  in  volume  measured  in  A 
gives  the  percentage  of  each  constituent 
gas. 

The  connections  to  A   are  made  through 
the   glass   stop   cocks   M   and   the   capillary 


*SOLUTIONS  FOR  ORSAT  APPARATUS 

For  absorbing  CO2 — Caustic  Potash.  Dissolve  one  part  by  weight  of  caustic  potash  in  two  and  one- 
half  parts  of  water. 

For  absorbing  O — Pyrogallol.  Dissolve  one  part  by  weight  of  pyrogallic  acid  in  two  parts  of  hot  water, 
and  three  parts  of  caustic  potash  solution,  made  as  above  directed. 

For  absorbing  CO — Cuprous  Chloride.  Dissolve  one  part  by  weight  of  cuprous  chloride  in  seven  parts 
of  hydrochloric  acid,  then  add  two  parts  of  copper  clippings  and  let  stand  for  twenty-four  hours,  after- 
wards adding  three  parts  of  water  before  use. 


APPLICATION    OF    FORMULAS  AND    RULES 


185 


tube  C.  The  movement  of  the  gases  is 
produced  by  lowering  or  raising  the  bottle 
L,  which  is  connected  to  the  lower  part  of 
A  by  the  rubber  tube  S,  and  is  partially 
filled  with  water.  When  a  measurement 
is  taken,  the  level  of  the  water  in  A  and  L 
must  be  the  same,  so  that  all  measurements 
are  taken  at  atmospheric  pressure.  A  con- 
stant temperature  of  the  gas  in  A  is  main- 
tained by  the  water  in  the  surrounding 
cylinder  shown. 

The  sample  is  drawn  into  the  apparatus 
through  the  cock  B,  which  also  serves  to 
connect  the  capillary  tube  to  the  atmos- 
phere, the  latter  connection  being  through 
the  spindle  of  the  cock;  this  permits  the 
removal  of  any  excess  of  gas  above  100  cc 
that  may  have  been  drawn  into  A.  Before 
the  sample  is  drawn,  the  vessels  D,  E  and  F 
should  have  their  respective  liquids  raised 
to  the  cocks  M  (which  can  then  be  closed, 
and  the  atmospheric  pressure  acting  through 
the  other  leg,  which  is  open,  will  keep  them 
filled) ;  the  burette  A  and  the  capillary  tubes 
should  be  filled  with  water  up  to  the  cock  B. 
All  this  can  easily  and  quickly  be  done  by 
raising  and  lowering  L,  and  opening  and 
closing  cocks  M  and  B.  The  absorption 
of  oxygen  and  carbon  monoxide  is  very  slow, 
and  the  gas  should  be  passed  back  and  forth 
a  number  of  times  until  a  reduction  of 
volume  is  no  longer  indicated. 

As  the  pressure  of  the  gases  in  a  flue  is 
less  than  the  atmospheric  pressure,  they 
will  not,  of  themselves,  flow  through  the 
rubber  or  metal  tubing  connecting  to  the 
analyzing  apparatus;  but  by  filling  the 
instrument  two  or  three  times  and  discharg- 
ing it  into  the  atmosphere  through  cock  B, 
the  air  can  be  removed  from  the  connecting 
tubing  and  a  sample  of  the  gas  be  obtained. 
For  rapid  work,  an  aspirator  can  be  used 
for  drawing  the  gas  from  the  tube  in  a  con- 
stant stream.  If  this  is  used  there  is  less 
danger  of  an  admixture  of  air.  It  is  some- 
times desirable  to  take  a  sample  that  repre- 
sents an  average  during  half  an  hour  or  an 
hour,  and  in  this  case  a  metal  or  glass  vessel 
with  a  stop -cock  at  both  top  and  bottom, 
and  filled  with  water,  can  be  connected 
through  the  upper  stop-cock  to  the  flue,  and 
the  bottom  cock  then  be  opened.  The  water 
will  gradually  drip  out,  drawing  the  gas  into 


the   vessel.     The    time  taken    to    fill    it    can 
be  regulated  by  the  lower  cock. 

The  result  of  a  flue-gas  analysis  depends 
both  on  the  manner  and  time  of  taking  the 
sample,  and  to  get  at  the  average  compo- 
sition of  the  gas,  a  number  of  determinations 
should  be  made  on  samples  from  different 
parts  of  the  flue. 


FIG.  42.     ORSAT  APPARATUS  FOR  FLUE-GAS  ANALYSIS 

The  analysis  made  by  the  Orsat  apparatus 
is  volumetric;  if  the  analysis  by  weight  is 
required  it  can  be  .found  from  the  volumetric 
analysis  as  follows: 

Multiply  the  percentages  by  volume  by  the 
molecular  weight  of  the  gas,  and  divide  by  the 
sum  of  all  the  products;  the  quotient  will  be 
the  percentage  by  weight. 

The  molecular  weights  are  as  follows: 
Carbon  dioxide      ....      44 
Carbon  monoxide.      .      .      .      28 
Oxygen       ......      32 

Nitrogen 28 

Application  of  Formulas  and  Rules — 
Pocahontas  coal  used  in  a  furnace  was 
composed  of  82.1  %  Carbon 

4.25%  Hydrogen 
2.6  %  Oxygen 
6.      %  Ash 


186 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


C02  =10.6% 

O    =  10. 
CO    =  o. 

N  =79.4 
analysis      by 


The  flue-gas  analysis  gave 
Carbon  dioxide    .... 
Oxygen     ... 
Carbon  monoxide 
Nitrogen  (by  difference) 

Determine : — The  flue-gas 
weight,  the  amount  of  air  required  for  perfect 
combustion,  the  actual  weight  of  air  per 
pound  of  coal,  the  weight  of  flue-gas  per  pound 
of  coal,  the  heat  loss  in  chimney  if  gases  are 
discharged  at  500°  F.,  and  the  ratio  of  the 
air  supplied  per  pound  of  coal  to  that  theo- 
retically required.  Solution: 

Weight  of  air  for  perfect  combustion= 
(  .821  .026  ) 

34.56XJ  •*•    «*" >  = 

v          O 


Weight  of  flue-gases  per  pound  of  coal= 
18.64+1 -.06=19.58  Ibs.     (Formula  46) 

Heat  lost  in  flue-gases  per  pound  of  coal= 
.24X19.58  X  (500-60)  =  2063.25  B.  T.  U.'s. 
(Formula  49) 

The  coal  contains  about  14,500  B.  T.  U.'s, 

2  06^     2  C 

so  there  is  — ^  =14.2%  of  the  heat   lost 

14,500 

in  the  flue-gases. 

Ratio  of  air  supplied  to  that  required= 

^^ =1.90  (Formula  48.) 

.794-. 10X3- 782 

This  may  also  be  calculated  from  the  first  two 
18.64 


.0425- 


=  10. 8 1  Ibs. 


results    above, 


1.72,    the    difference 


(Formula  43) 

Actual  weight  of  air  per  pound  of  coal= 
794 


3-Q32X- 
( Formula  44) 


106— .00 


X  .821-18.64 Ibs. 


10.81 

between  this  ratio  and  that  obtained  from 
Formula  [48]  being  due  to  inaccuracies  in 
either  the  flue-gas  or  coal  analysis,  or  in  both. 
Table  56  shows  the  method  of  converting 
a  flue-gas  analysis  by  volume  into  an  an- 
alysis by  weight. 


TABLE  56 
ANALYSIS    OF    FLUE-GASES 


GAS. 

Analysis  by 
Volume. 

Molecular  Weight. 

Volume  X 
Molecular  Weight. 

Analysis  by  Weight. 

Carbon  dioxide       .      .    (CO  2  ) 
Carbon  monoxide  .      .      (CO) 

10.  6 
0.0 
10.  0 

79-4 

12   +  2   X   l6 
12  +  l6 
2    X    l6 

2    X    14 

466  .  4 

0.0 

320  .  o 

2223  .  2 

466.4 

5% 

o% 

7% 
8% 

3.009.6 
O  .  O 

3009  .  6 
320.0 

Nitrogen     .      ..     .     '.        (N) 

3009.6 

2223  .  2 

—  «  i 

f.      '3 
3009.6 

Total     .    . 

.     3009.6 

Steam  Boiler  Efficiency 


The  efficiency  of  a  boiler  is  the  ratio  be- 
tween the  heat  units  utilized  in  production 
of  steam,  and  the  heat  units  contained  in 
the  fuel  used.  But  whenever  solid  fuel  such 
as  coal  is  used,  it  is  impossible  to  prevent 
a  portion  of  it  from  falling  through  the 
grates,  where  it  mixes  with  the  ashes  without 
burning,  and  generates  no  heat.  The  boiler 
itself  cannot  justly  be  charged  with  failure 
to  absorb  the  heat  value  represented  by  the 
fuel  wasted  through  the  grates,  but  the  boiler 
owner  must  pay  for  the  fuel  so  wasted,  and 
is  justified  in  charging  this  waste  to  the 
combination  of  boiler  and  furnace.  The  heat 
supplied  to  the  boiler  is  that  due  to  the  com- 
bustible actually  burned,  irrespective  of  how 
much  may  be  dropped  through  the  grates. 
In  consequence  two  efficiencies  may  be  de- 
termined, viz.: 

(1)  Efficiency  of  the  boiler= 

Heat  absorbed  per  Ib.  of  combustible      [51] 
Heat  value  of  one  Ib.  of  combustible* 

(2)  Efficiency    of    boiler    and    grate= 
Heat  absorbed  per  pound  of  fuel       [52] 
Heat  value  of  one  pound  of  fuel, 

The  first  is  of  value  in  comparing  relative 
performances  of  boilers  apart  from  the  par- 
ticular kind  of  grate  used  under  them;  the 
second  is  of  value  in  comparing  performances 
of  different  kinds  of  fuels,  grates,  etc.,  under 
the  same  boiler.  If  the  loss  of  fuel  through 
the  grates  could  be  wholly  obviated,  then 
the  two  efficiencies  would  be  identical,  as 
in  case  of  a  boiler  fired  with  oil.  Thus,  if  a 
coal  contained  90%  combustible,  efficiency 
( i )  would  be 

Heat  absorbed  per  Ib.  of  fuel  X .  90 
Heat  value  of  one  Ib.  of  fuel X.  90 

which  reduces  to  efficiency  (2).  Similarly, 
efficiency  (2)  will  in  any  particular  case 
figure  out  the  same  whether  the  fuel  be  taken 
as  dry  coal,  or  coal  as  fired  with  its  content 
of  moisture.  Example: — If  the  coal  con- 
tained 3%  of  moisture,  efficiency  (2)  would  be 


Heat  absorbed  per  pound  of  dry  coal X 0.9 7 
Heat  value  of  one  Ib.  of  dry  coal  X 0.97 

Here  the  content  of  moisture  cancels  out, 
hence  efficiency  (2)  may  be  based  on  either 
dry  coal,  or  coal  as  actually  fired. 

Assume  the  following  data : 
Steam  pressure  by  gauge      .      .      .      149  Ibs. 
Temperature  of  feed  water    .      .      .        84°    F. 
Weight  of  coal  as  fired     .      .      .      .  7152  Ibs. 
Percentage  of  moisture  in  coal    .      .      .96 

Total  ash  and  refuse 286  Ibs. 

Percentage  of  moisture  in  steam      .      0.5 
Total  water  evaporated  ....  68664  Ibs. 

Analysis  of  the  coal,  by  weight. 

Moisture 0.96% 

Ash 2.19 

Carbon f ..      .      .87.76 

Hydrogen 4 . 1 1 

Oxygen ,  nitrogen  and  sulphur    .      .4.98 


of 


100.00% 

dry    coal    by 


Heat    value    per    pound 
calorimeter  15450  B.  T.  U. 

The  factor  of  evaporation  for  the  condi- 
tions named  is  1.182,  hence  the  equivalent 
evaporation  from  and  at  212°  is  68664  X 
1.182  =  81161  Ibs.,  and,  corrected  for  the 
moisture  present,  is  .5%  less,  or  80755  Ibs. 
of  dry  steam  from  and  at  212°.  This  contains 
80755X966  =  78,009,330  B.  T.  U. 

The    dry    coal    fired    was 

7152-  (  .0096X7152)  =  7083  Ibs. 
The  ash-pit  contained  286  Ibs.  of  ash  and 
refuse,  whence  the  combustible,  or  coal  dry 
and  free  from  ash,  was  7083—286=6797  Ibs. 
The  heat  units  in  the  steam  are  therefore: 

Per  pound  of  coal  as  fired, 

78,009,330  =  I0907  B  T  n   (a) 


Per  pound  of  dry  coal, 
78,609,330 


7083 

Per  pound  of  combustible, 
78.009,330 


6797 


=  11477  B.T.  U.    (c) 


*By  combustible  is  here  meant  that  part  of  the  fuel  dry  and  free  from  ash.  Nitrogen  and  oxygen  are 
thus  included.  Neither  is  combustible  in  strict  accuracy,  but  custom  has  included  them,  as  they  form 
part  of  the  volatile  content  of  coal. 

187 


COMBUSTION  RATE  CHART 


DIAGONAL  LINES  REPRE- 
SENT POUNDS  OF  COAL 
BURNED  PER  SQUARE  FOOT 
OF  GRATE  PER  HOUR 


RATIO  OF  HEATING  SURFACE  TO  GRATE  SURFACE 


4.5 


85% 


u.        8 


BOILER  EFFICIENCY  CHART 


DIAGONAL    LINES 

REPRESENT  PERCENTAGES 

OF  EFFICIENCY 


5.6 


4.5 


,000  8,000 


9,000  10, 

HEAT  VALUE  IN 


000  11,000  12,000  13,000          14,000  15,000  1 6,000 

B.T.U.  PER  POUND  OF  FUEL  OR  COMBUSTIBLE. 


DISTRIBUTION    OF    HEAT    LOSSES 


191 


The  heat  value  per  pound  of  dry  coal,  as 
given  by  the  calorimeter,  is  15450.  Since 
the  moisture  in  the  coal  amounted  to  0.96%, 
the  heat  value  per  pound  of  "coal  as  fired" 
is  (100—  .oo96)X  15450  =  15302  B.  T.  U. 
The  analysis  shows  that  the  combustible 
portion  of  the  coal  amounts  to  87. 76+4. n  + 
4.98=96.85%  of  the  original  coal,  and 
15302-^.9685  =  15800  nearly.  Hence  the  heat 
values  of  the  fuel  are : 

Per  pound  of  coal  as  fired      15302  B.  T.  U.  (d) 
Per  pound  of  dry  coal      .      15450  B.  T.  U.  (e) 
Per  pound  of  combustible     15800  B.  T.  U.   (f) 
and  the  efficiencies  are : 
Based    on    coal    as 

fired  ....  10907-^-15302  =  71.28% 
Based  on  dry  coal  .  11013-^15450  =  71.28% 
Based  on  combust- 

ble      ....       11477-^-15800  =  72.64% 

Efficiency  and  Combustion=Rate  Charts 

—The  charts  on  pages  188  and  189  illustrate 
the  relation  existing  between  heat  value, 
evaporation,  efficiency,  heating  surface,  grate 
surface  and  combustion  rate,  as  factors  in 
steam  boiler  operation,  and  the  two  charts 
may  be  used  separately  or  jointly,  as  the 
conditions  of  the  problem  may  determine. 
Only  one  assumption  is  made,  viz.:  that 
ten  square  feet  of  heating  surface  represent 
one  boiler  horse-power,  and  that,  in  conse- 
quence, at  rating  a  boiler  evaporates  3.45 
pounds  of  water  (from  and  at  212°)  per 
hour  per  square  foot  of  heating  surface. 
Given  the  equivalent  evaporation  and  calor- 
ific value  of  the  fuel  in  any  case,  the  efficiency 
(of  the  boiler,  or  of  boiler  and  grate,  accord- 
ing as  the  evaporation  and  heat-value  are 
referred  to  combustible  or  to  coal  as  fired] 
is  shown  by  the  diagonal  passing  nearest 
the  intersection  of  the  lines  corresponding 
to  the  other  two  quantities;  in  the  right- 
hand  chart  the  corresponding  combustion 
rates,  at  rating  and  50%  above  rating,  are 
indicated  on  the  diagonal  nearest  the  in- 
tersection of  the  lines  for  the  equivalent 
evaporation  and  ratio  of  heating  surface  to 
grate  surface. 

If,  on  the  other  hand,  it  is  desired  to  ob- 
tain a  certain  rate  of  evaporation  with  a 
boiler  of  known  ratio  of  heating  surface  to 
grate  surface,  the  right-hand  chart  will 
indicate  the  amount  of  fuel  per  square  foot 


of  grate  which  must  be  burned  to  obtain 
such  evaporation,  and  by  reference  to  the 
left-hand  chart  the  heat  value  of  the  coal 
necessary  to  obtain  this  evaporation  at  any 
given  efficiency  may  be  determined. 

Distribution  of  Losses — The  efficiency  of 
a  boiler,  whether  based  on  the  combustible 
or  the  dry  coal,  will  be  found  to  range  from 
50%  to  80%,  and  in  some  cases  higher.  The 
difference  between  the  actual  efficiency  and 
1 00%  is  the  loss  occurring  in  the  conversion 
of  the  heat  energy  of  the  coal  into  that  con- 
tained in  the  steam.  This  loss  is  made  up 
of  items  as  follows: 

(1)  Loss  of  fuel  through  the  grate. 

(2)  Unburned    fuel    carried    beyond    the 
bridge  wall    in    the    form  of    soot    or  small 
particles. 

(3)  The   heat  required   to   raise   the  tem- 
perature  of   the   moisture    in    the  coal  from 
atmospheric  temperature  to  212°,  to  evapo- 
rate it  at  that  temperature,  and  to  superheat 
to  the  flue-gas  temperature  the  steam    thus 
formed. 

(4)  The  loss  due  to  the  presence  of  hydro- 
gen in  the  fuel,  which  forms  water  which  must 
be  evaporated  and  superheated  as  in  Item  3. 

(5)  Superheating  the  moisture  in  the  air 
supplied,    from    the    prevailing    atmospheric 
temperature  to  that  of  the  flue-gases. 

(6)  Heating  the   products  of   combustion 
(excepting  the  steam)   to  the    flue-gas  tem- 
perature. 

(7)  The   loss   due  to   incomplete  combus- 
tion when  carbon  burns  to  carbon  monoxide 
(CO)   instead   of    to   carbon   dioxide    (CO2), 
and  when  the  volatile  gases  pass  out  through 
the  stack  unburned. 

(8)  The  loss  due  to  radiation  of  heat  from 
the  boiler  and  furnace. 

It  would  require  an  elaborate  test  to  as- 
certain each  one  of  those  items,  and  in 
practise  it  is  customary  to  summarize  them 
as  follows: 

(a)  Loss  due  to  moisture  in  the  coal; 
this  refers  to  the  hydroscopic  moisture  only. 
Loss  due  to  moisture  formed  by  burning 
the  hydrogen  in  the  fuel.  These  two  losses 
in  B.  T.  U.= 

(gH+VV)  [212-^  +  965. 8  +0.48(^-2 12)] 

In  which  H  and  W  are  the  proportional 
part,  referred  to  the  combustible,  of  the 


192 


THE    STIRLING   WATER-TUBE   SAFETY  BOILER 


hydrogen  and  water;  /  the  fire  room  tem- 
perature, and  T  the  breeching  temperature. 

(b)  Loss  due  to  heat  carried  off  in  chim- 
ney gases,  equal  in  B.T  U.  to  (T-t)Xo.  24* 
X  weight  of  gases  per  pound  of   combustible. 

(c)  Loss   due   to   incomplete    combustion 
of  carbon,  forming  CO,  equal  in   B.  T.  U.  to 

10.150  CO 
(CO,  +  CO) 

in  which  CO,  and  CO  are  percentages  by 
volume  of  the  flue-gases  and  C  is  proportion- 
al part  of  carbon  in  the  combustible. 

(d)  Heat  unaccounted  for,  equal  to  total 
heat  generated,  less  the  sum  of  that  utilized 
and  the  losses  (a),  (b)  and  (c).     This  includes 
the    losses  under    items  (2,)  (5)  and    (8)  as 
.above,  and  loss  from  un  consumed  gases. 

A  schedule  of  these  losses  is  called  a  "Heat 
Balance."  To  make  it  requires  an  evapora- 
tive test  of  the  boiler,  an  analysis  of  the 
flue-gases,  an  ultimate  analysis  of  the  coal, 
and  a  calorimeter  determination  of  its  heat 
value. 

Example:  To  illustrate  the  application  of 
the  foregoing  the  following  data  from  a 
test  of  a  517^  H.  P.  Stirling  boiler  may  be 
taken  : 


Steam  pressure,  absolute  ... 

Temperature  of  stack 

"  fire-room 
"  feed-water 

Weight  of  coal  as  fired,  per  hour, 

Moisture  in  coal 

Weight  of  dry  coal,  per  hour   . 

Ash  arid  refuse,  per  hour    . 

Ash  and  refuse,  per  hour 

Combustible  per  hour 

Calorific  value  of  combustible  per 

Analysis  of  dry  coal 


lb.«.  per  sq.  in. 
deg.  F. 


175.7 

481  .o 
87. 
76.7 

153.  i 

2-7 

1489.8 

113.6 

7.6 

1376. 2 
15696 


Evaporation,  actual,  per  hour 
Moisture  in  steam  .... 
Analysis  of  flue-gases  . 


.       .       Ibs. 

per  cent. 
.      .      Ibs. 
.      .      Ibs. 

percent. 
.      .      Ibs. 
pound      B.  T.  U. 

C=  83  . 84%  by  weight. 
H=  4.72 
O=  3-77 
N=  1.65 
S=  1.07 
Ash=  4.95 

100  .00% 

.       .      Ibs.  14577-9 

per  cent.  .  7 

002=13.5%  by  volume 

O=   5.8 

CO=  o.i 

N=8o.6 


100.0% 

Since  the  steam  contains  .75%  moisture, 
the  dry  steam  per  hour  amounts  to  14,577  .9 
X  ( ioo.  oo-  o.  7 5)  =  1 4, 468. 6  Ibs. 


The  absolute  steam  pressure  being  157.7 
Ibs.  and  the  temperature  of  the  feed  76.7°, 
the  factor  of  evaporation  is  1.1911;  and 
the  equivalent  evaporation  per  hour  from 
and  at  2 12°, is  14,468.6X1 .1911  =  17,233.5  Ibs. 

J7. 233. 5-1376. 2  =  12.523  U.  E.|  per  Ib. 
of  combustible 

17.233.5-1489.8=11.568  U.  E.  per  Ib.  of 
dry  coal. 

12.523X965.7  =  12093.4  B.  T.  U.  in  steam 
per  Ib.  of  combustible 

11.568X965.7.1=11171.2  B.  T.  U.  in  steam 
per  Ib.  of  dry  coal 

The  calorific  value  of  the  fuel,  per  pound 
of  combustible,  is  15696.  The  combustible 
amounts  to  100-4. 95^=95  .05%  of  the  dry 
coal,  whence  the  calorific  value  of  'i  Ib.  of 
the  dry  coal  is  9505X15696  =  14919  B.  T.  U. 
and  the  two  efficiencies  are, 

Efficiency  of    boiler  -  =.  7704 

15696 

=  77  .04  per  cent,  based  on  the  combustible. 

Efficiency  of  boiler  and   grate= — 

14919 

.7487  =  74.87  per  cent.,  based  on  the  dry  coal. 
The  heat  losses  are  calculated  as  follows: 

(a)  Loss   due  to  moisture  in   coal.     The 
content  of  moisture  referred  to  combustible 
is  2.7-89.88!!  =.03,  and  this  loss  is  .03X1X212- 
76.7)+966J  +0.48  (48i-2i2)]=36.9o  B.T.U. 

From  the  ultimate  analysis,  the  hydrogen 
in  the  coal  is  seen  to  be  4.72%,  therefore  the 
loss  due  to  burning  hydrogen  is, 
9X^472  X   [(212-76.7)+  966+0.48  (481  - 

212)1=522.5  B.  T.  U. 

(b)  To  compute  the  loss  of  heat  in  the 
dry  chimney  gases  per  pound  of  combustible, 
the  weight  of  the  gases  must  first  be  ascer- 
tained. 

From  formula  [46]  page  183  the  weight  of 
gases  per  pound  of  coal  as  fired  is, 
3.032  XXC    , 


C02+CO 


3.032X80.6X0.8384 


+  (1-0.0495) 


=  16.01  Ibs. 
Hence  the  weight  of  flue-gases  per  pound  of 


*Specific  heat  of  chimney  gas.  fU.  E.=Units  of  evaporation.  See  p.  72.  £965. 8  would  be  more 
exact,  but  966  is  recommended  in  the  Code  of  1885.  gNote  that  this  is  the  real  ash  as  determined 
from  the  ultimate  analysis,  hence  is  the  value  to  use  in  determining  the  B.  T  U.  per  pound  of  dry  coal. 
|| Combustible  consumed  per  hour-:- coal  as  fired  per  hour.  Note  the  difference  between  the  combus- 
tible as  a  per  cent,  of  the  coal  as  fired,  and  of  the  dry  coal. 


VARIATION    OF    EFFICIENCY    WITH    RATE    OF    DRIVING 


193 


combustible    is     16.01-^  .8988=17.81     Ibs., 
therefore  the  loss  of  heat  in  stack    is 

17.81X0.24  (48i-87)  =  i684  B.  T.   U. 
(c)     Loss  due  to  incomplete  combustion. 
From  the  ultimate  analysis  the  per  cent,  of 
carbon  in  the  combustible  is 

-=88 .2%,  hence  this  loss  is 


100-4.95 

o. 1X0. 882+10150 


=  65.35    B.T.  U. 


I3-5+0-1 

(d)  The  above  determined  losses  amount 
to  36.90  +  522.5  +  1684+65.35=2308.75  B. 
T.  U.  The  heat  absorbed  by  the  boiler  per 
pound  of  combustible  is  12093.4  B.  T.  U., 
hence  the  total  heat  accounted  for  is  12,093  . 4 
+  2,308.75=14,402.15  B.  T.  U.  But  the 
calorific  value  of  one  pound  of  combustible 
is  15,696  B.  T.  U.,  hence 

Heat   unaccounted    for 

=  15.696-14,402.15  =  1293.85  B.  T.  U. 

The  heat  balance  should  be  arranged  thus: 

HEAT  BALANCE 

Total  heat  of  i  Ib.  of  Combustible  = 
15696   British  Thermal  Units. 


DISTRIBUTION    OP    THE    HEAT. 

B.   T.   U. 

PERCENT 

i.     Heat  absorbed  by  the  boiler 

I  2,093.4 

77  .04 

2.     Loss  clue  to  moisture  in  coal 

36.0 

•  24 

3.     Loss  due  to  moisture  formed  by  the 

burning  of  hydrogen         .... 
4.     Loss  due  to  heat  carried  away  in  dry 

522.5 

3-33 

chimney-gases      

1,684.0 

IO-73 

5.     Loss  due  to  incomplete  combustion 

65     ^ 

6.     Unaccounted  for     

8   24 

Totals  

15,696  .OO 

100  .00 

Application  of  the  Heat  Balance- 
Whenever  a  boiler  test  supplies  data  for  making 
a  heat  balance,  it  should  be  made,  particu- 
larly if  the  boiler  performance  is  considered 
unsatisfactory.  The  distribution  of  the  heat 
is  thus  determined  and  any  extraordinary 
loss  can  be  detected  and  steps  be  taken  to 
reduce  it. 

The  heat  absorbed  to  produce  steam  will 
range  from  50  to  80  per  cent.,  or  more,  50% 
being  very  poor  efficiency  and  80%  very 
high;  in  judging  efficiencies  the  character  of 
fuel  must  always  be  considered,  since  an 
efficiency  that  would  be  regarded  as  high  for 
one  fuel  might  be  very  low  for  another. 


The  loss  due  to  moisture  in  the  coal  is 
small  but  appreciable.  Therefore  coal  should 
be  kept  under  roof,  and  should  not,  as  in 
some  plants,  be  wetted  before  using. 

The  largest  heat  loss  is  due  to  the  chimney- 
gases.  The  factors  affecting  this  are  the 
amount  of  gas  and  the  temperature  at  which 
it  leaves  the  boiler.  There  is  a  lower  limit 
to  the  amount  of  gas,  fixed  by  the  minimum 
air  supply  with  which  thorough  combustion 
may  be  obtained.  This  limit  usually  is  18 
pounds  of  air  per  pound  of  coal.  The  limit 
may  be  still  lower  when  burning  gas  or  oil. 
If  the  air  supply  is  too  small,  the  loss  due 
to  carbon  burning  to  carbon  monoxide  will 
be  increased.  The  stack  temperature  is 
limited,  with  natural  draft,  to  not  much  less 
than  450°,  since  a  lower  temperature  causes 
loss  of  draft  and  a  low  heat  transfer  from 
gases  to  water  in  the  boiler.  Artificial  draft 
and  economizers  may  reduce  these  limits,  and 
whether  or  not  they  can  save  enough  to 
compensate  for  the  extra  outlay  is  a  problem 
to  be  solved  for  each  particular  case. 

Variation  of  Efficiency  with  Rate  of 
Driving — Under  any  set  of  conditions  there 
is  one  rate  of  evaporation  per  square  foot 
at  which  the  greatest  efficiency  will  be 
developed,  and  there  will  be  a  falling  off  for 
both  higher  and  lower  rates  of  evaporation. 
The  grade  of  fuel,  skill  with  which  it  is  fired, 
the  air  supply,  condition  of  boiler  surfaces, 
and  temperature  of  steam  and  of  feed  water, 
are  some  of  the  factors  which  affect  the  re- 
sult, hence  no  exact  figure  for  the  rate  of 
evaporation  which  will  give  the  greatest 
efficiency  can  be  given.  Under  average 
conditions  it  varies  from  3  to  4  pounds  per 
square  foot  of  heating  surface  from  and  at 
212°  per  hour  for  water-tube  boilers.  As 
the  rate  is  increased  the  drop  in  efficiency 
varies  greatly  for  different  types  of  boiler 
and  the  kind  of  fuel.  The  matter  is  of  the 
utmost  importance  in  plants  where  the  boilers 
must  be  operated  at  high  rates  of  evapora- 
tions for  several  hours  daily  to  carry  peak 
loads.  The  Stirling  boiler  falls  off  in  effi- 
ciency, as  the  load  is  increased,  much  less 
rapidly  than  other  types,  because  of  the 
efficient  absorption  of  heat  in  the  rear  tube 
bank  where  the  feed  water  enters.  See 
"Possibility  of  Driving  at  Both  High  and 
Low  rates  of  Evaporation,"  page  27. 


Horse-Power  Rating  of  Boilers 


Work,  as  the  term  is  used  in  mechanics, is 
the  overcoming  of  a  resistance  through  space. 
The  unit  of  work  is  the  foot-pound. 

Power  is  the  rate  at  which  work  is  done,  or 
is  the  amount  of  work  done  in  one  unit  of 
time.  The  unit  of  power  in  general  use 
among  steam  engineers  is  the  Horse- 
power,* which  is  equivalent  to  33,000 
foot-pounds  per  minute,  or  the  work  done 
in  lifting  33,000  pounds  i  foot  high,  or  33 
pounds  1,000  feet  high,  or  1,000  pounds  33 
feet  high,  etc.,  in  one  minute. 

Horse=Power  of  Boilers — Boilers  for 
land  use  are  usually  rated  in  "horse-power," 
and  few  terms  used  in  engineering  are  more 
often  misunderstood. 

A  boiler  when  in  service  does  not  move, 
hence*it  does  no  work  in  the  sense  in  which  this 
word  is  used  in  mechanics,  therefore  it  has 
no  power.  What  it  really  does  is  to  generate 
steam  which  acts  as  a  vehicle  to  convey  the 
energy  of  the  fuel,  in  the  form  of  heat,  to 
an  engine  which  converts  that  heat  into 
work  and  develops  power.  If  every  engine 
developed  precisely  the  same  power  from 
an  equal  amount  of  heat,  the  boiler  might 
conveniently  be  designated  as  a  boiler 
having  the  same  horse-power  as  the  engine; 
though  inaccurate,  the  statement  could 
through  custom  be  interpreted  to  mean  that 
the  boiler  is  of  just  the  capacity  required 
to  supply  the  steam  necessary  to  generate 
the  given  horse-power  in  an  engine.  Un- 
fortunately, engines  of  different  sizes  and 
types  require  widely  different  amounts  of 
steam  to  produce  the  same  power,  hence  a 
boiler  which  could  supply  enough  steam  to 
produce  500  H.  P.  in  one  engine  might  be 
able  to  supply  only  enough  to  produce  300 
H.  P.  in  another  engine  which  is  of  less 
economical  design. 


Present  Meaning  of  (Stationary)  Boil= 
er  Horse=Power — To  obviate  the  confusion 
resulting  from  an  indefinite  meaning  of  the 
term  boiler  horse-power,  the  judges  in  charge 
of  boiler  trials  at  the  Centennial  Exposition 
ascertained  that  a  good  engine  of  the  then 
prevailing  types  required  about  30  Ibs.  of 
steam  per  hour  per  horse-power  developed. 
In  order  to  establish  a  relation  between  the 
engine  power  and  the  size  of  boiler  needed  to 
furnish  steam  to  develop  that  power,  they 
recommended  that  an  evaporation  of  30 
pounds  of  water  per  hour  from  an  initial 
feed  temperature  of  100°  F.  to  steam  of 
70  pounds  gauge  pressure  be  considered  as 
one  boiler  horse-power.  The  standard  thus 
laid  down  has  been  generally  accepted  by 
American  engineers,  and  whenever  in  this 
countryt  the  term  boiler  horse-power  is 
used  in  connection  with  stationary  boilers! 
without  special  definition,  it  is  to  be  under- 
stood as  having  the  meaning  above  defined. 

To  permit  easy  comparison  of  results  of 
boiler  trials,  it  is  usual  to  reduce  them  all 
to  a  basis  of  equivalent  evaporation  from 
and  at  212°  F.  One  boiler  horse-power  as 
above  defined  is  equivalent  to  an  evapora- 
tion from  and  at  212°  F.  of  34.486  Ibs.  of 
water, §  or  practically  34.  5  Ibs.,  hence, 

One  boiler  horse-power  is  equal  to  an  evapora- 
tion per  hour  of  30  Ibs.  of  water  from  100°  F. 
to  steam  at  jo  pounds  pressure;  or  is  equal 
to  an  evaporation  of  34. $  pounds  of  water  per 
hour  from  and  at  212°  F.  It  is,  therefore, 
purely  a  measure  of  evaporation,  and  not 
of  power. 

Selection  of  Boilers  to  Operate  an  En= 
gine  of  given  Power — To  determine  the 
rated  horse-power  of  boiler  necessary  to  devel- 
op a  given  power  from  an  engine,  it  is  neces- 
sary to  determine  the  amount  of  steam  re- 


*The  French  horse-power  (cheval)  is  seventy-five  kilogrammeters  per  second  =  75X7.233  foot-pounds  = 
542.5  foot-pounds  per  second,  or  somewhat  less  than  that  used  by  English-speaking  nations,  which  is 
equal  to  550  foot-pounds  per  second.  Hence, 

One  horse-power    =1.0139  cheval 
One  cheval  =    .9864  horse-power 

fin  other  countries  boilers  are  usually  rated,  not  in  horse-powers,  but  by  specifying  the  quantity  of 
water  they  are  to  be  capable  of  evaporating  from  and  at  212°,  or  under  other  conditions  which  can  be 
reduced  to  equivalent  evaporation  from  and  at  212°. 

JWhen  the  horse-power  of  marine  boilers  is  stated  it  generally  refers  to  and  is  synonymous  with  the 
horse-power  developed  by  the  engines  which  receive  steam  from  the  boilers. 

§See  "Equivalent  evaporation  from  and  at  212°,"  page  69. 

13  IQ5 


196  THE    STIRLING    WATER-TUBE    SAFETY    BOILER 

TABLE  57 

INDICATED  HORSE-POWER  PER  BOILER  HORSE-POWER  FOR  VARIOUS 
AMOUNTS   OF   STEAM   PER   I.  H.  P.  AXD    FACTORS   OF   EVAPORATION 


Factor  of 

Evaporation. 

1  .  02 

I  .  Ot 

1.07 

5 

I  . 

i  .  i 

'-5 

Actual  Water 
Consumption 
of  Engines 
per  I.  H.  P. 
per  Hour. 

Equivalent 
Evaporation 
per 
I.  H.  P. 

Engine 
H.P. 
per 
Boiler 
H.P. 

Equivalent 
Evaporation 
per 
I.  H.P. 

Engine 
H.P. 
per 
Boiler 
H.P. 

Equivalent 
Evaporation 
per 
I.  H.  P. 

Engine 
H.P. 
per 
Boiler 
H.P. 

Equivalent 
Evapor- 
ation per 
1.  H.  P. 

Engine 
H.  P. 
per 
Boiler 
H.  P. 

Equivalent 
Evapor- 
ation per 
I.  H.  P. 

Engine 
H.P. 
per 
Boiler 
H.P. 

ro. 

10.  25 

3.36 

10.5 

3-28 

10.75 

3-21 

I  I  .  O 

3  -  i  3 

ii  .25 

3.06 

to.  S 

10.  76 

3.20 

1  1  .  02 

3-  13 

11.30 

3.05 

11-55 

.98 

ii  .81 

•92 

ii  . 

11.27 

3.06 

n-55 

.98 

11.83 

.91 

I  2  .  IO 

-85 

12.37 

•  79 

ii.  S 

11.78 

•  03 

12  .07 

.85 

12.38 

.78 

12  .  65 

-73 

12.94 

.67 

I  2  . 

12.30 

.80 

I  2  .  6O 

•73 

12  .90 

.67 

13.  20 

.61 

13.5 

.56 

12.5 

I  2  .  8l 

.69 

13.12 

.62 

13-44 

.56 

13.75 

-50 

14.06 

•45 

13- 

1  .3  -  3  2 

•59 

I.i.65 

•52 

13.98 

•49 

14.30 

•  4i 

14.  62 

•  36 

13.25 

13.58 

•  54 

I3-9I 

•47 

14-  25 

.42 

14.57 

•  37 

14.91 

•31 

I3-S 

I3.84 

.49 

14.  I? 

•43 

14.52 

.38 

I4.S5 

•  32 

15.19 

•27 

13-75 

14.09 

•45 

14-43 

•37 

14.72 

•33 

15.12 

.28 

15-47 

•  23 

14. 

14-35 

•40 

14.  70 

•33 

15.05 

.29 

15-4 

•  24 

15.75 

•  '9 

14-  25 

14.  60 

.36 

14.96 

.29 

15.32 

•  25 

15  .67 

.  20 

16.03 

•  IS 

14-5 

14.86 

•32 

15.22 

•  25 

15-59 

.  2  1 

15.95 

.  K) 

16.31 

.  12 

14.  7.  S 

15.12 

.28 

15.48 

.  2  I 

15-86 

-  I  7 

l6.  22 

.  1  2 

16.59 

.08 

IS- 

15.38 

•  24 

15-75 

.  18 

16.13 

•  13 

16.5 

.09 

16.87 

•OS 

IS-  25 

15-63 

.  21 

16.  01 

•  IS 

1  6.  40 

.   IO 

10.77 

.  06 

17.16 

.01 

15-5 

15.89 

•  17 

16.27 

.  I  2 

16.67 

.07 

17  -05 

.03 

17  -45 

.98 

15.75 

16.14 

-  13 

16.53 

.08 

16.94 

.04 

[7.32 

99 

17.72 

•95 

16. 

16.40 

.  IO 

16.80 

•05 

17  .  20 

.  OI 

17  .  OO 

.96 

18.00 

•92 

16.  25 

16.65 

.  06 

17  .06 

.  O  I 

17-47 

.98 

17-87 

•  94 

18.28 

.89 

16.5" 

16.91 

•03 

17-32 

.98 

17-74 

•94 

i  8  .  i  S 

-1)0 

18.56 

.86 

16.75 

17.16 

.00 

17-58 

•95 

iS.OI 

.91 

18.42 

.87 

18.84 

•83 

17. 

17.42 

.98 

17-85 

•  93 

I  8    28 

.88 

18.7 

-84 

19.12 

.80 

17-25 

17.67 

•95 

i8.ii 

.91 

18-55 

.86 

18.97 

.82 

19.40 

•77 

17-5 

17-93 

•  92 

18.37 

•87 

18.81 

.83 

19-  25 

.So 

19.69 

•75 

17-75 

18.  19 

.89 

18.63 

-84 

19-  13 

.80 

I9.52 

•  77 

19.97 

.73 

18. 

18.45 

.87 

1  8  .  90 

.81 

19-35 

•  77 

19.8 

•74 

20  .  25 

.70 

18.25 

18.70 

.85 

19  .  16 

•78 

I  9  .  6  2 

-75 

20  .  07 

•  71 

20.53 

•67 

18.5 

18.96 

.82 

19-43 

•76 

19.89 

•  73 

20.35 

.69 

20.81 

•65 

i8-75 

19  .  22 

•  79 

19.69 

•  74 

20.15 

•  7i 

20.  62 

•  67 

2  I  .  09 

•63 

19. 

19.48 

.76 

19-95 

•72 

30.42 

.69 

20.9 

•  65 

21  .37 

.61 

19-  25 

19-73 

•  74 

2O.  21 

.70 

20.  69 

.67 

21.17 

•63 

21.65 

•59 

iQ-5 

19.99 

-7i 

20.47 

.67 

2O  .  96 

.64 

21  .45 

.61 

21  .93 

•57 

19-75 

2O  .  24 

.69 

20.73 

.65 

21  .  23 

.62 

21.72 

•59 

22.22 

•55 

30. 

20.  50 

-67 

21  .OO 

.63 

21  .  50 

.60 

22  .  O 

•  57 

32.  50 

•S3 

30.  25 

2O  .  76 

.65 

21  .  26 

.61 

21  .77 

.58 

22  .  27 

•  54 

22.78 

•  Si 

20.  S 

21  .02 

.63 

21  .52 

•59 

22  .  04 

.56 

22.55 

•  52 

23.06 

-49 

20.75 

21.27 

.61 

21  .78 

•  57 

22.31 

•  54 

22.82 

•  51 

23.34 

•47 

31  . 

21.52 

.60 

22.05 

.56 

22.58 

•  53 

23.  10 

.49 

23.62 

.46 

21.25 

21  .77 

•  58 

22.31 

•  54 

22.84 

•  Si 

23.37 

•47 

23.91 

•44 

31-5 

22  .03 

.56 

22.57 

•  52 

23.11 

•  49 

23.65 

-45 

24.  20 

42 

21.75 

22  .  29 

-54 

22.83 

•  50 

33.38 

•  47 

23.92 

•43 

24.47 

•  40 

22. 

22.55 

•52 

23.  10 

.40 

23.65 

.46 

24.2 

•  42 

24-75 

•  39 

22.  S 

25  .06 

•49 

23.62 

•  45 

24-  19 

•  42 

24.75 

•  39 

25  -31 

-36 

23- 

23.58 

.46 

24.  15 

-42 

24.73 

•  39 

25.3 

•  36 

25.87 

•  33 

23-5 

24.09 

•  43 

24.67 

.39 

25  •  26 

.36 

25.85 

•33 

26  .43 

•  30 

24- 

24.60 

•  40 

25  .  20 

-36 

25.80 

.33 

26.4 

.30 

27  .OO 

.28 

24-S 

25.11 

25.72 

.33 

26.  34 

.30 

26.95 

•  27 

27.5<' 

•25 

25  • 

25.63 

-34 

26  .  25 

.  3  I 

26.88 

.  2.S 

27  .5 

•  25 

28.   12 

•  23 

25-5 

26.  14 

•  32 

26.77 

•  29 

27  -42 

.26 

28.05 

.  23 

28.68 

.  21 

26. 

26.(,5 

•  29 

27.30 

.  20 

27.95 

.  23 

28.6 

.  20 

29.  25 

.18 

26.5 

27  .  l6 

•  27 

27.82 

•  24 

28.49 

.  21 

29.  15 

.  i  8 

29  .  80 

.16 

27- 

27.68 

.24 

28.35 

.  22 

29.03 

•  19 

29.70 

.  i  6 

30.37 

•  14 

27  -  5 

28.  10 

.  22 

28.87 

.  2O 

29.  56 

•  17 

30.  25 

•  14 

30.43 

.  I  2 

28. 

28.70 

.  2O 

29.40 

.  17 

30  .  10 

•  14 

30.8 

.  i  i 

31  •  50 

.09 

2Q. 

29.72 

.  16 

30.45 

•  13 

31.18 

.  I  I 

3i-9 

.08 

32.62 

05 

30. 

30.75 

.  I  2 

3  i  .  50 

.00 

32.25 

.08 

33-0 

.05 

33  •  73 

.02 

31- 

31.78 

.08 

32.55 

-05 

33.32 

.03 

34-  i 

.02 

34.87 

•99 

32. 

32.80 

.°5 

33.6o 

.02 

34.40 

.OO 

35-2 

.98 

36.0 

.96 

33- 

33.83 

.02 

34.65 

•99 

35.47 

•97 

36.3 

.95 

37-12 

•93 

34. 

34.85 

.99 

35-70 

36.55 

.94 

37-4 

.02 

38.25 

.00 

35- 

35.87 

.96 

36.75 

•93 

37-02 

.91 

38.5 

.S,, 

39-37 

.87 

36. 

36.90 

•93 

37.8o 

.90 

38.70 

.89 

39-6 

.87 

40.  5 

-85 

37- 

37.92 

.90 

38.85 

.88 

39-77 

.86 

40.7 

.84 

41  .02 

.82 

38. 

38.95 

.88 

39-90 

.86 

40.85 

.84 

41  .8 

.82 

42.75 

.80 

39- 

39.98 

.86 

40.95 

.84 

41  .92 

.82 

42.9 

.80 

43-87 

•79 

40. 

41  .00 

.84 

42  .  oo 

.82 

43.00 

.80 

44-0 

.78 

45. 

-77 

41  • 

42.03 

.82 

43.05 

.80 

44-07 

-78 

45-1 

.76 

46.  12 

•75 

42. 

43.05 

.80 

44-  10 

.78 

45-15 

.76 

46.  2 

•  74 

47  •  25 

•  73 

43- 

44.08 

.78 

45-  IS 

.76 

46.  22 

.74 

47  -3 

•  72 

48.57 

•  7i 

44- 

45-  1° 

.76 

46.  20 

.74 

47-30 

.72 

48.4 

•  70 

40  -  5 

.69 

45- 

46  .  i  2 

•  75 

47.25 

•  73 

48.37 

•  71 

49-5 

.69 

50.  62 

.68 

RELATION    BETWEEN    INDICATED    AND    BOILER   HORSE-POWER 

TABLE  57 — CONTINUED 

INDICATED  HORSE-POWER  PER  BOILER  HORSE-POWER  FOR  VARIOUS 
AMOUNTS  OF  STEAM  PER   I.  H.  P.  AND   FACTORS  OF  EVAPORATION 


197 


Factor  of 

I  .  I 

1.17 

I  .  2 

I  .  2 

25 

I  .  2 

5 

Evaporation. 

Actual  Water 
Consumption 
of  Engines 
p-r  I.  H.  P. 
per  Hour. 

Equivalent 
Evaporation 
per 
I.    H.  P. 

Engine 
H.  P. 
per 
Boiler 
H.  P. 

Equivalent 
Evaporation 
per 
I.  H.  P. 

Engine 
H.  P. 
per 
Boiler 
H.P. 

Equivalent 
Evaporation 
per 
I.  H.P. 

Engine 
H.P. 
per 
Boiler 
H.P. 

Equivalent 
Evapor- 
ation per 
I.  H.  P. 

Engine 
H.P. 
per 
Boiler 
H.P. 

Equivalent 
Evapor- 
ation per 
I.  H.  P. 

Engine 
H.P. 
per 
Boiler 
H.  P. 

o  . 

I  I  .5 

2-99 

H.75 

-93 

12.0 

.87 

12.25 

2.81 

12.5 

.76 

o.  5 

12.57 

2.85 

12.33 

•79 

12.6 

•73 

12.86 

2  .  69 

13.12 

.67 

[  . 

12.  65 

2.72 

12.92 

.67 

13-  2 

.61 

13-47 

2.  57 

13.75 

.58 

r  .  5 

13-22 

2  .  60 

13.51 

•  55 

13-8 

•  SO 

14  .  08 

2-45 

14.35 

•  44 

2  . 

1.5.8 

2.49 

14.  10 

•  44 

14-4 

•39 

14.7° 

2.35 

15.0 

•  30 

2  -  5 

14.38 

2  .40 

14.69 

•  35 

15-0 

•  30 

iS-31 

2.  25 

IS  .62 

.  21 

3  . 

J4-95 

2.31 

15-28 

•  2S 

15.  6 

.  21 

15-92 

2.  l6 

16.  25 

.  12 

1  .1  •  2  5 

15.23 

2  .  26 

iS-57 

.  21 

15.9 

-17 

l6.  22 

2.12 

16.56 

.08 

13.5 

15.52 

2.22 

15-86 

•17 

16.  2 

•  13 

16.53 

2.08 

16.87 

•04 

i  ..  •  7  5 

15.81 

2.  l8 

16.  15 

•  13 

16.5 

.09 

16.84 

2  .  04 

17.19 

.01 

14- 

16  .  10 

•  14 

16.45 

.09 

16.8 

-05 

I7-IS 

2  .  OI 

17-5 

•  97 

14-  25 

16.  38 

.  10 

16.  74 

•05 

17.1 

.01 

17-45 

1.97 

17.81 

•93 

14-  5 

16.67 

.  06 

17.04 

.  O2 

17.4 

.98 

17.76 

1-94 

18.12 

.90 

I4-7S 

16.96 

.  02 

17-33 

.98 

17-7 

-94 

18.06 

I  .  90 

18.44 

•87 

IS- 

17  •  25 

-99 

17.63 

•  95 

18. 

-91 

18.37 

1.87 

18.75 

.84 

15.25 

17.53 

.96 

17.92 

.92 

18.3 

.88 

18.68 

1.84 

19  .  06 

.81 

15-5 

17.82 

•93 

l8.  22 

.89 

18.6 

•  8s 

18.98 

1.81 

19.37 

.78 

15-75 

1  8  .  1  1 

.90 

18.51 

.86 

18.9 

.82 

19.  29 

1.78 

19  .  66 

•  75 

16. 

18.40 

•87 

iS.So 

•  83 

19.2 

-79 

19  .6 

1.76 

20. 

•  72 

16.25 

18.68 

.84 

19.10 

.80 

19-5 

•  76 

19.9 

1-73 

20.31 

.69 

16.5 

18.97 

.81 

19-39 

-77 

19.8 

•74 

2O  .  21 

i  .70 

20.62 

.67 

l6.75 

IQ  .  26 

.78 

19.68 

-74 

20  .  i 

•  7i 

20.  51 

1.67 

20.93 

•65 

17- 

19.55 

•76 

19.98 

•  72 

20  .  4 

.69 

20.82 

1.65 

21  .  25 

.62 

17  •  25 

19.83 

•  73 

20.  27 

.70 

20.  7 

.66 

21.12 

i  .  62 

21  .  56 

•59 

17-5 

2O  .   I  2 

•71 

20.56 

.68 

21  . 

.64 

21  -43 

i  .  60 

21.87 

•57  . 

17-75 

20.  41 

.68 

20.85 

-65 

21.3 

.62 

21.74 

.1.58 

22.18 

•  55 

18. 

2O  .  7O 

.66 

21.15 

.63 

21.6 

•59 

22.05 

1.56 

22.50 

•53 

18.25 

20  .  g8 

.64 

21  .45 

.60 

21.9 

•  57 

22.35 

i  -54 

22.  8l 

•  Si 

18.5 

21.27 

.62 

21  .74 

.58 

22  .  2 

•  55 

22.66 

1-52 

23.  12 

•49 

18.75 

21.56 

.60 

22  .0.3 

-56 

22.5 

•  S3 

22  .  96 

1.50 

23-43 

•47 

10  . 

ai.Ss 

•59 

22.33 

-55 

22.8 

•  5i 

23.27 

1.48 

23-75 

•  45 

ig.  25 

22.   13 

•  5f> 

22.62 

-54 

23-1 

.40 

23-57 

i  .46 

24.06 

•43 

19.5 

22  .42 

•  54 

22.91 

-52 

23.4 

•  47 

23-88 

1.44 

24-37 

.41 

ig.75 

22.71 

•  Si 

23.21 

•49 

23.7 

•  45 

24-  19 

1.42 

24.68 

•39 

20. 

23.0 

•  49 

23.  5° 

•  47 

24  .  o 

•  43 

24.  50 

1.41 

25  .00 

^38 

20.  2S 

23.28 

•  47 

23.  79 

-45 

24.3 

.41 

24.81 

1.39 

25.31 

.36 

20.5 

23-57 

•  45 

24.  08 

•  43 

24.6 

-40 

25.11 

1-37 

25  .62 

•34 

20.  75 

23.86 

.43 

24-37 

•  4i 

24.9 

•39 

25-41 

1-35 

25.93 

•33 

21  . 

24-  15 

.42 

24-67 

•  40 

25.2 

25-72 

1-34 

26.  25 

•  31 

21.25 

24-43 

.40 

24.96 

•  37 

25-  5 

•  35 

26.02 

1.32 

26.56 

.29 

21  .  5 

24-  72 

•  39 

25.26 

.36 

25.8 

•  34 

26.33 

I-3I 

26.87 

.28 

21.75 

25.01 

-38 

25-  56 

-35 

26.1 

•  32 

26.64 

1.30 

27.18 

•27 

22  . 

25.3 

.36 

25-85 

•  33 

26.4 

•  3i 

26.95 

1.28 

27.5 

.26 

22.5 

25.87 

-33 

26.43 

•  31 

27. 

.28 

27-56 

1.25 

28.  12 

•  23 

23- 

26.  45 

-30 

27  .02 

.28 

27  .  6 

•  25 

28.17 

I  .  22 

28.75 

.  20 

23-5 

27  .02 

-  27 

27  .  61 

•  25 

28.2 

.  22 

28.78 

I.I9 

29-37 

-17 

24- 

27.6 

-25 

28  .  20 

-  23 

28.8 

•  19 

29.40 

I.  17 

30. 

•IS 

24.  5 

28.  17 

.  22 

28.78 

.  20 

29.4 

•  17 

30.01 

I.  14 

30.62 

.  12 

25. 

28.75 

.  2O 

29-37 

.17 

30. 

•  IS 

30.62 

I  .  12 

31-25 

.  IO 

25.5 

29-32 

.  18 

29.96 

-  IS 

30.6 

•  13 

31-23 

I  .  IO 

31.87 

.08 

26. 

29.9 

-  IS 

30.55 

.  I  2 

31.2 

.  I  I 

31.85 

I.  08 

32.S 

.06 

26.  5 

30.48 

-  13 

31  •  13 

.  IO 

31.8 

.09 

32.46 

I  .06 

33-12 

•04 

27- 

3i  -°5 

.  1  1 

31  .72 

.00 

32.4 

.06 

33.07 

I  .04 

33-75 

.02 

27.5 

31  -62 

.00 

32.31 

•07 

33. 

.04 

33.63 

I  .02 

34-37 

.OO 

28. 

32.2 

.06 

32.90 

.04 

33.6 

.02 

34-30 

I  .OO 

35- 

.98 

29. 

33-35 

.02 

34.07 

.  oo 

34-8 

•99 

35-52 

•97 

36.25 

•  93 

30. 

34-5 

•  90 

35-25 

•  97 

36. 

.96 

36.75 

•  94 

37-  S 

-92 

31  . 

35.65 

.Q6 

36.42 

.94 

37-2 

.92 

37-97 

.91 

38.7S 

.89 

32. 

36.8 

•  93 

37-6o 

•92 

38.4 

.89 

39-20 

.88 

40. 

.86 

33- 

37-95 

.90 

38.77 

.89 

39-6 

.87 

40.42 

.85 

41.25 

.84 

34. 

39-  I 

.88 

39-9S 

.87 

40.8 

.85 

41.65 

.83 

42.5 

.8r 

35- 

40.  25 

.85 

41.12 

.84 

42. 

.82 

42.87 

.80 

43-75 

.78 

36. 

41  .4 

-83 

42.3 

.81 

43.2 

.80 

44.  10 

.78 

45- 

•  76 

37- 

42.55 

.80 

43-47 

.78 

44-4 

•78 

45.32 

.76 

46.25 

•  74 

38. 

43-7 

.78 

44.65 

.76 

45-6 

•76 

46.55 

•  74 

47-5 

•72 

39- 

44.85 

•  77 

45.82 

•  75 

46.8 

•  74 

47.77 

•  72 

48.75 

.70 

40. 

46. 

•  75 

47-00 

•  73 

48. 

•  72 

49.0 

•  70 

50. 

.68 

41- 

47-  iS 

•  73 

48.18 

-7i 

49-2 

•  70 

SO.  22 

.68 

51.2 

.66 

42. 

48.3 

•  71 

49-35 

.69 

S0.4 

.63 

51-45 

.66 

52.5 

.65 

43. 

49-45 

.69 

50-52 

.68 

51.6 

.67 

52.67 

.65 

53-75 

.64 

44. 

50.6 

-67 

Si  -70 

.66 

52.8 

.65 

53.90 

.63 

S5- 

•  63 

45. 

51-75 

.66 

52.87 

-65 

54. 

.63 

55-12 

.62 

56.25 

.62 

198 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


quired  to  produce  the  given  power  in  the  en- 
gine, then  ascertain  the  size  of  boiler  requisite 
to  generate  this  steam.  The  determination 
of  the  amount  of  steam  needed  by  engines 
of  various  sizes,  types  and  conditions,  can  be 
done  only  by  making  actual  trials,  or  by 
reference  to  trials  on  similar  engines. 


sure,  engine  speed,  and  point  of  cut-off.  In 
modern  plants  using  large  compound  con- 
densing engines  with  high  pressure  steam 
one  boiler  horse-power  may  be  sufficient  to 
develop  two  engine  horse-power,  including 
the  steam  necessary  to  operate  pumps  and 
other  auxiliaries.  A  simple  engine  of  ordi- 


TABLE  58 
STEAM   CONSUMPTION,    POUNDS   PER   INDICATED    HORSE    POWER* 


Steady 

Loads. 

Variable  Loads. 

Extreme  Variations, 
Railway  Work,  etc., 

TYPE  OF  ENGINK. 

50  to  125  per  cent. 

o  to  150  per  cent. 

Non- 
Condensing. 

Condensing. 

Non- 
Condensing. 

Condensing. 

Non- 
Condensing. 

Condensing. 

High  Speed,  simple   . 

32 

28 

34 

3° 

36 

31 

High  Speed,  compound  . 

23 

18 

25 

21 

27 

22  .5 

Slow  Speed,  simple    . 

25 

21 

28 

23 

31-5 

26.5 

Slow  Speed,  compound  . 

2O 

J5 

22-5 

18 

26 

23 

High  Speed,  triple  exp.   . 

J7-5 

13 

20 

16 

Slow  Speed,  triple  exp.  . 

14-5 

I2-5 

17 

T5 

Table  58  gives  a  rough  approximation 
of  the  steam  required  per  indicated  horse- 
power for  engines  of  different  types : 

Such  performance  can  be  expected  only 
from  engines  of  good  grade.  Plain  slide 
valve  engines  may  use  55  to  60  Ibs.  per 
hour  per  H.  P.  All  similar  tables  are  neces- 
sarily very  approximate,  since  the  steam 
consumption  will  vary  with  the  steam  pres- 


nary  build,  operated  non-condensing,  will 
require  more  than  one  boiler  horse-power 
per  engine  horse-power,  while  direct  acting 
steam  pumps  will  require  as  much  as  two 
or  more  boiler  horse-power  per  engine  horse- 
power. Consequently,  when  designing  a 
steam  plant  it  is  necessary  to  determine 
from  the  type  of  engine  the  steam  that  will 
be  required,  and  to  make  the  necessary 


TABLE  59 

REQUIRED   HOURLY    EVAPORATION    PER   BOILER    HORSE-POWER 
AT  VARIOUS  FEED  TEMPERATURES  AND   STEAM   PRESSURES 


STEAM  PRESSURE  IN   POUNDS  BY  GAUGE. 


f 

DllaAM  r^lS.C*OOU  IS.C/  UN  rWUi>IL/O  DX  VJrtUVJfO. 

o 

10 

20 

3° 

40 

50 

60 

7° 

80 

90 

IOO 

I  IO 

I2O 

130 

140 

150 

160 

170 

180 

190 

200 

50 

19.51 

29.29 

29.14 

29.02 

28.92 

28.84 

28  77 

28.70 

28.64 

28.59 

28.54 

28.49 

28.45 

28.41 

2837 

2833 

28.29 

28.26 

28.23 

28.20 

28.17 

60 

29  77 

29  55 

29.40 

29.28 

29.18 

29.09 

29.02 

28.95 

28.89 

28.84 

28.79 

28.74 

28.69 

28.65 

28.61 

285? 

28.54 

28.51 

28.48 

28  45 

28.42. 

70 

30.04 

29.81 

29.66 

29  54 

29-44 

29  35 

29.27 

29  21 

29.15 

29.09 

29  04 

28.99 

28.94 

28.90 

28  86 

28.82 

28.78 

28.75 

28.72 

28.69 

28.66 

80 

3031 

30.08 

29-93 

29.80 

29.70 

29.61 

29  53 

29.46 

29.40 

29  34 

29.29 

29.24 

29.19 

29  15 

29.11 

29.07 

29  03 

29  oo 

28.97 

28.94 

28.91 

90 

3°  59 

3°  36 

30.20 

30-07 

29-97 

29.88 

29.80 

29  73 

29.67 

29.61 

29  55 

29-50 

29  45 

29.41 

29  37 

29  33 

29.29 

29.25 

29.22 

29.19 

29  16 

100 

3088 

30.64 

30-47 

3034 

3°  24 

30  15 

30.07 

30.00 

29  93 

29.87 

29  82 

29  77 

29.72 

29.67 

29  63 

29  59 

29  55 

29  5' 

29.48 

29-45 

29.42 

I  10 

3'  '7 

3°-93 

30  76 

3063 

3°  52 

30.43 

3034 

30.27 

30.20 

3°  '4 

30.09 

30.04 

29.99 

29.94 

29  90 

29.86 

29.82 

29.78 

29  74 

29.71 

29.68 

I  20 

31.46 

31.22 

3'  05 

3°  Qi 

30.80 

30  7' 

3°  63 

30.55 

30.48 

30.42 

3036 

30  3' 

30.26 

30.21 

3°  '7 

3°  '3 

30.09 

3005 

30.01 

29.98 

29  95 

'3° 

3'  ?6 

3'  S^ 

3'  34 

31.20 

3'  09 

3099 

30  9' 

3083 

30  76 

30  70 

30.65 

30.59 

30  54 

3°  49 

3°45 

30  41 

30  37 

3033 

30.29 

30  25 

30.22 

140 

32  07 

31.82 

3'  64 

3>  So 

3138 

3r-29 

31.20 

31.12 

31-05 

30  99 

30  93 

30.88 

3083 

30.78 

30  73 

30.69 

30  65 

30.61 

30.57 

30-53 

3°  50 

150 

3*  39 

,52.12 

3  '-94 

31.80 

31.68 

3L58 

3>  So 

3'  42 

31-35 

31.28 

31  22 

31-17 

31.12 

3'  07 

31  02 

3097 

3°93 

30.89 

30.85 

30.81 

3078 

1  60 

32  7' 

32  44 

32.26 

32.11 

3'  99 

3'89 

31.80 

3"  72 

3'.6s 

3i  58 

3'  52 

31.46 

3'.4> 

3'  36 

3'  3' 

3"  27 

3'  23 

3'  "9 

J'-'S 

31.11 

31.08 

170 

33  °3 

32-76 

32-58 

32  43 

32-31 

32.20 

32.11 

32  03 

31.96 

3'-89 

J'-83 

3'-77 

3I-7I 

31  66 

31.61 

3'  56 

3'  52 

31-48 

3'-44 

31  40 

31-37 

180 

33-37 

33  °9 

32.90 

32-75 

32  63 

32  52 

32  43 

32.34 

32.27 

32.20 

32  M 

32.08 

32.02 

3'  97 

3"  92 

3'  87 

3'  83 

3'-79 

3'-75 

31  7" 

3'  67 

190 

33-7' 

33  43 

33-23 

3308 

32-95 

32.84 

32-75 

3266 

32.59 

32.52 

32  45 

32.39 

3»  33 

32.28 

32  23 

32.18 

32-.M 

32.10 

32.06 

32.02 

3'98 

100 

34  06 

33-77 

33  57 

33  4i 

33  28 

33-'7 

33o8 

32  99 

32  9' 

32.84 

32  77 

32.71 

32  65 

32.60 

32  55 

32  50 

32  45 

32  41 

32  37 

32  33 

32  11 

111 

34  49 

34  18 

33.98 

32.80 

33  69 

33  58 

33.48 

33-39 

33.31 

33-24 

33-»7 

33  I' 

33  05 

33  99 

32  94 

32  89 

32.84 

32.80 

32.76 

32.72 

32  68 

*  See  "Economy  of  Modern  Engine  Room."     Engineering  Magazine,  Oct.  1896. 


BOILER    HORSE-POWER    TABLES 


199 


allowance  for  auxiliaries  and  boilers  un- 
dergoing cleaning,  and  then  determine  the 
corresponding  boiler  capacity. 

Number  of  Units  Required — The  re- 
quired boiler  horse-power  having  been  determ- 
ined, the  number  of  units  into  which  it  should 
be  divided  will  depend  upon  the  character  of 
the  work  to  be  done.  If,  for  example,  there 
is  a  day  load  which  is  about  double  the  night 
load,  the  boiler  units  should  be  so  propor- 
tioned that  half  the  boiler  power  can  be  cut 


fuel,  while  exhibiting  good  economy;  and 
further,  the  boiler  should  be  capable  of 
developing  at  least  one-third  more  than  its 
rated  power  to  meet  emergencies  at  times 
when  maximum  economy  is  not  the  most 
important  object  to  be  attained." 

Boiler  Horse=Power  Tables—  When  the 
feed  water  temperature  and  the  gauge  pres- 
sure are  known,  the  water  per  boiler  horse- 
power hour  may  be  taken  directly  from 
Table  59.  When  the  actual  weight  of 


2,500  HORSE-POWER  OF  STIRLING  BOILERS,  COTTON  STATES  AND  INTERNATIONAL  EXPOSITION, 

ATLANTA,  GEORGIA 


out  at  night.  When  fixing  the  number  of 
units,  provision  should  be  made  for  reserve 
power  to  allow  for  repairs,  cleaning  boilers, 
and  emergencies. 

Allowance  for  Overload — The  Commit- 
tee on  Trials  of  Steam  Boilers  in  their  re- 
port to  the  American  Society  of  Mechanical 
Engineers,  said — "A  boiler  rated  at  any 
stated  number  of  horse-powers  should  be 
capable  of  developing  that  power  with 
easy  firing,  moderate  draft,  and  ordinary 


steam  required  by  an  engine  per  indicated 
.  horse-power  hour,  and  the  steam  pressure 
and  boiler  feed  temperature  are  known,  the 
boiler  horse-power  per  engine  horse-power 
can  be  taken  without  calculation  from  Table 
57.  First,  from  Table  16  determine  the 
factor  of  evaporation,  then  refer  to  the 
column  under  that  factor  in  Table  57  and 
the  tabular  value  opposite  the  water  con- 
sumption of  the  engine  is  the  boiler  horse- 
power per  engine  horse-power. 


Rules  for  Conducting  Boiler  Trials 


Whenever  a  boiler  test  is  made  it  is  desirable 
that  the  results  be  recorded  in  such  shape 
as  to  permit  ready  comparison  with  other 
tests.  In  this  country  boiler  tests  are 
usually  conducted  according  to  the  latest 
code  of  rules  formulated  by  a  committee  of 
the  American  Society  of  Mechanical  Engineers, 
hence  this  code  is  here  reproduced  complete 
except  some  portions  which  touch  upon 
matters  more  fully  treated  elsewhere  in  this 
book,  and  to  which  the  reference  is  given  in 
each  case. 

RULES  FOR  CONDUCTING  BOILER  TRIALS 
CODE  OF   1899.* 

I.  Determine  at  the  Outset  the  specific  object 
of  the  proposed  trial,  whether  it  be  to  ascertain  the 
capacity   of  the  boiler,   its  efficiency   as   a   steam 
generator,  its  efficiency  and  its  defects  under  usual 
working  conditions,  the  economy  of  some  particular 
kind  of  fuel,  or  the  effect  of  changes  of  design,  pro- 
portion,   or    operation;    and    prepare   for   the    trial 
accordingly. 

II.  Examine  the  Boiler,  both  outside  and  inside; 
ascertain  the  dimensions  of  grates,  heating  surfaces, 
and  all  important  parts;  and  make  a  full  record, 
describing  the  same,  and  illustrating  special  features 
by  sketches.     The  area  of  heating  surface  is  to  be 
computed  from  the  surfaces  of  shells,   tubes,  fur- 
naces, and     fire-boxes  in  contact  with  the  fire  or 
hot  gases.     The  outside  diameter  of    water- tubes 
and  the  inside  diameter  of  fire-tubes  are  to  be  used 
in  the  computation.     All  surfaces  below  the  mean 
water  level  which  have  water  on  one  side  and  pro- 
ducts of  combustion  on  the  other  are  to  be  con- 
sidered as  water  heating  surface,  and  all  surfaces 
above  the  mean  water  level  which  have  steam  on 
one  side  and  products  of  combustion  on  the  other 
are  to  be  considered  as  superheating  surface. 

III.  Notice  the  General  Condition  of  the  boiler 
and  its  equipment,  and  record  such  facts  in  relation 
thereto  as  bear  upon  the  objects  in  view. 

If  the  object  of  the  trial  is  to  ascertain  the  maxi- 
mum economy  or  capacity  of  the  boiler  as  a  steam 
generator,  the  boiler  and  all  its  appurtenances 
should  be  put  in  first-class  condition.  Clean  the 
heating  surface  inside  and  outside,  remove  clinkers 


from  the  grates  and  from  the  sides  of  the  furnace. 
Remove  all  dust,  soot,  and  ashes  from  the  chambers, 
smoke  connections,  and  flues.  Close  air  leaks  in  the 
masonry  and  poorly  fitted  cleaning  doors.  See  that 
the  damper  will  open  wide  and  close  tight.  Test 
for  air  leaks  by  firing  a  few  shovels  of  smoky  fuel 
and  immediately  closing  the  damper,  observing 
the  escape  of  smoke  through  the  crevices,  or  by 
passing  the  flame  of  a  candle  over  cracks  in  the 
brickwork. 

IV.  Determine  the  Character  of  the  Coal  to  be 
used.     For  tests   of  the  efficiency  or  capacity  of 
the  boiler  for  comparison  with  other  boilers,   the 
coal  should,  if  possible,  be  of  some  kind  which  is 
commercially  regarded   as   a    standard.     For   New 
England  and  that  portion  of  the  country  east  of  the 
Allegheny    Mountains,    good    anthracite    egg   coal, 
containing  not  over  10  per  cent,  of  ash,  and  semi- 
bituminous    Clearfield    (Pa.),    Cumberland    (Md.), 
and  Pocahontas   (Va.),   are    thus  regarded.     West 
of    the   Allegheny    Mountains,    Pocahontas,    (Va.), 
and    New   River    (W.    Va.)     semi-bituminous,    and 
Youghiogheny  or  Pittsburg  bituminous  coals  are  rec- 
ognized as  standards. f     There  is   no  special  grade 
of  coal  mined  in  the  Western  States  which  is  widely 
recognized   as    of     superior  quality  or    considered 
as  a  standard  coal  for   boiler  testing.     Big  Muddy 
lump,  an  Illinois  coal  mined   in    Jackson  County, 
111.,  is    suggested     as     being     of    sufficiently  high 
grade    to    answer    these  requirements    in    districts 
where    it  is  more  conveniently  obtainable  than  the 
other  coals  mentioned  above. 

For  tests  made  to  determine  the  performance 
of  a  boiler  with  a  particular  kind  of  coal,  such  as 
may  be  specified  in  a  contract  for  the  sale  of  a 
boiler,  the  coal  used  should  not  be  higher  in  ash 
and  in  moisture  than  that  specified,  since  increase 
in  ash  and  moisture  above  a  stated  amount  is  apt 
to  cause  a  falling  off  of  both  capacity  and  economy 
in  greater  proportion  than  the  proportion  of  such 
increase. 

V.  Establish  the  Correctness  of  all  Apparatus 
used  in  the  test  for  weighing  and  measuring.     These 
are: 

1.  Scales  for  weighing  coal,  ashes,  and  water. 

2.  Tanks,  or  water-meters,  for  measuring  water. 
Water-meters,  as  a  rule  should  be  used  only  as  a 


*From  Volume  XXI.  of  the  Transactions  of  the  American  Society  of  Mechanical  Engineers. 

tThese  coals  are  selected  because  they  are  about  the  only  coals  which  possess  the  essentials  of  excellence  of  quality,  adaptability 
to  various  kinds  of  furnaces,  grates,  boilers,  and  methods  of  firing,  and  wide  distribution  and  general  accessibility  in  the  markets. 


202 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


check  on  other  measurements.     For  accurate  work, 
the  water  should  be  weighed  or  measured  in  a  tank. 

3.  Thermometers    and    pyrometers    for    taking 
temperatures  of  air,  steam,  feed-water,  waste  gases, 
etc. 

4.  Pressure  gauges,  draught  gauges,  etc. 

The  kind  and  location  of  the  various  pieces  of 
testing  apparatus  must  be  left  to  the  judgment  of 
the  person  conducting  the  test;  always  keeping  in 
mind  the  main  object,  that  is,  to  obtain  authentic 
data. 

VI.  See  that  the  boiler  is  thoroughly  heated  to 
its   usual   working   temperature   before    the    trial. 
If  the  boiler  is  new  and  of  a  form  provided  with  a 
brick  setting,  it  should  be  in  regular  use  at  least 
a  week  before  the  trial,  so  as  to  dry  and  heat  the 
walls.     If  it  has  been  laid  off  and  become  cold,  it 
should  be  worked  before  the  trial  until  the  walls 
are  well  heated. 

VII.  The    boiler   and    connections    should    be 
proved  to  be  free  from  leaks  before  beginning  a 
test,    and    all    water    connections,    including   blow 
and  extra  feed  pipes,  should  be  disconnected,  stopped 
with  blank  flanges,  or  bled  through  special  open- 
ings beyond  the  valves,  except  the  particular  pipe 
through  which  water  is  to  be  fed  to  the  boiler  during 
the  trial.     During  the  test  the  blow-off  and  feed 
pipes  should  remain  exposed  to  view. 

If  an  injector  is  used,  it  should  receive  steam 
dirctly  through  a  felted  pipe  from  the  boiler  being 
tested.* 

If  the  water  is  metered  after  it  passes  the  injector, 
its  temperature  should  be  taken  at  the  point  where 
it  leaves  the  injector.  If  the  quantity  is  deter- 
mined before  it  goes  to  the  injector  the  temperature 
should  be  determined  on  the  suction  side  of  the 
injector,  and  if  no  change  of  temperature  occurs 
other  than  that  due  to  the  injector,  the  temperature 
thus  determined  is  properly  that  of  the  feed  water. 
When  the  temperature  changes  between  the  injector 
and  the  boiler,  as  by  the  use  of  a  heater  or  by 
radiation,  the  temperature  at  which  the  water  enters 
and  leaves  the  injector  and  that  at  which  it  enters 
the  boiler  should  all  be  taken.  In  that  case  the 
weight  to  be  used  is  that  of  the  water  leaving  the 
injector,  computed  from  the  heat  units  if  not  di- 
rectly measured,  and  the  temperature,  that  of  the 
water  entering  the  boiler. 


Let  w=weight    of   water  entering  the  injector. 
•x  =  "   steam 

^j=heat    units  per  pound  of  water   entering 

injector. 
/?2=heat    units  per  pound  of  steam   entering 

injector. 
/z3=heat    units  per  pound  of    water  leaving 

injector. 
Then  zy+.T=weight  of  water  leaving   injector. 


See  that  the  steam  main  is  so  arranged  that  water 
of  condensation  cannot  run  back  into  the  boiler. 

VIII.  Duration  of  the  Test  —  For  tests  made  to 
ascertain    either    the    maximum    economy    or    the 
maximum  capacity  of  a  boiler,  irrespective  of  the 
particular  class  of  service  for  which  it  is  regularly 
used,  the  duration  should  be  at  least  ten  hours  of 
continuous    running.      If    the    rate    of    combustion 
exceeds  25  pounds  of  coal  per  square  foot  of  grate 
surface  per  hour,  it  may  be  stopped  when  a  total 
of  250  pounds  of  coal  has  been  burned  per  square 
foot  of  grate. 

In  cases  where  the  service  requires  continuous 
running  for  the  whole  24  hours  of  the  day,  with 
shifts  of  firemen  a  number  of  times  during  that 
period,  it  is  well  to  continue  the  test  for  at  least 
34  hours. 

When  it  is  desired  to  ascertain  the  performance 
under  the  working  conditions  of  practical  running, 
whether  the  boiler  be  regularly  in  use  24  hours  a 
day  or  only  a  certain  number  of  hours  out  of  each 
24,  the  fires  being  banked  the  balance  of  the  time, 
the  duration  should  not  be  less  than  24  hours. 

IX.  Starting  and  Stopping  a  Test  —  The  con- 
ditions of  the  boiler  and  furnace  in  all  respects  should 
be,  as  nearly  as  possible,  the  same  at  the  end    as 
at  the  beginning  of  the  test.     The  steam  pressure 
should   be   the   same;   the  water  level  the    same; 
the  fire  upon   the  grates  should  be  the  same   in 
quantity  and  condition;  and  the  walls,  flues,  etc., 
should  be  of  the  same  temperature.     Two  methods 
of    obtaining    the    desired    equality    of    conditions 
of  the  fire  may  be  used,   viz.;  those  which  were 
called  in  the  Code  of  1885  "the  standard  method" 
and    "the    alternate    method,"    the    latter    being 
employed  where  it  is  inconvenient  to  make  use  of 
the  standard  method.  f 


*In  feeding  a  boiler  undergoing  test  with  an  injector  taking  steam  from  another  boiler,  or  from  the  main  steam  pipe  from 
several  boilers,  the  evaporative  results  may  be  modified  by  a  difference  in  the  quality  of  the  steam  from  such  source  compared  with 
that  supplied  by  the  boiler  being  tested,  and  in  some  cases  the  connection  to  the  injector  may  act  as  a  drip  for  the  main  steam 
pipe.  If  it  is  known  that  the  steam  from  the  main  pipe  is  of  the  same  pressure  and  quality  as  that  furnished  by  the  boiler  under- 
going the  test,  the  steam  may  be  taken  from  such  main  pipe. 

tThe  Committee  concludes  that  it  is  best  to  retain  the  designations  "standard"  and  "alternate,"  since  they  have  become  widely 
known  and  established  in  the  minds  of  engineers  and  in  the  reprints  of  the  Code  of  1885.  Many  engineers  prefer  the  "alternate" 
to  the  "standard"  method  on  account  of  its  being  less  liable  to  error  due  to  cooling  of  the  boiler  at  the  beginning  and  end  of  a  test. 


KEEPING   THE    RECORDS 


203 


X.  Standard  Method  of  Starting  and  Stopping 
a  Test — Steam  being  raised  to  the  working  pres- 
sure, remove  rapidly  all  the  fire  from  the  grate,  close 
the  damper,  clean  the    ash-pit,  and   as   quickly   as 
possible  start  a  new  fire  with  weighed  wood  and 
coal,  noting  the  time   and    the   water   level*  while 
the    water    is    in    a    quiescent    state,    just    before 
lighting  the  fire. 

At  the  end  of  the  test  remove  the  whole  fire, 
which  has  been  burned  low,  clean  the  grates  and 
ash-pit,  and  note  the  water  level  when  the  water 
is  in  a  quiescent  state,  and  record  the  time  of 
hauling  the  fire.  The  water  level  should  be  as 
nearly  as  possible  the  same  as  at  the  beginning 
of  the  test.  If  it  is  not  the  same,  a  correction  should 
be  made  by  computation,  and  not  by  operating  the 
pump  after  the  test  is  completed. 

XI.  Alternate  Method  of  Starting  and  Stopping 
a    Test — The     boiler    being    thoroughly    heated 
by  a  preliminary  run,   the  fires  are  to  be  burned 
low  and  well  cleaned.     Note  the  amount  of  coal 
left  on  the  grate  as  nearly  as  it  can  be  estimated; 
note  the  pressure  of  steam  and   the  water  level. 
Note  the  time  and  record  it  as  the  starting  time. 
Fresh  coal  which  has  been  weighed  should  now  be 
fired.     The  ash-pits  should    be  thoroughly  cleaned 
at  once  after  starting.      Before  the  end  of  the  test 
the  fires  should  be  burned  low,  just  as  before  the 
start,  and  the  fires  cleaned  in  such  a  manner  as  to 
leave  a  bed  of  coal  on  the  grates  of  the  same  depth, 
and  in  the  same  condition,  as  at  the  start.     When 
this  stage  is  reached,  note  the  time  and  record  it  as 
the    stopping    time.     The    water   level    and    steam 
pressures   should  previously   be   brought   as   nearly 
as  possible  to  the  same  point  as  at  the  start.     If 
the  water  level  is  not  the  same  as  at  the  start,  a 
correction  should  be  made  by  computation,   and 
not  be  operating  the  pump  after  the  test  is  com- 
pleted. 

XII.  Uniformity  of   Conditions — In   all   trials 
made  to  ascertain  maximum  economy  or  capacity, 
the    conditions    should    be    maintained    uniformly 
constant.     Arrangements  should  be  made  to  dis- 
pose of  the  steam  so  that  the  rate  of  evaporation 
may   be   kept   the   same   from   beginning   to    end. 
This  may  be  accomplished  in   a  single  boiler  by 
carrying  the  steam  through  a  waste-steam    pipe, 
the  discharge  from  which  can  be  regulated  as  de- 
sired.    In  a  battery  of  boilers,  in  which  only  one 
is  tested,   the  draft  may  be  regulated  on  the  re- 
maining boilers,   leaving   the   test  boiler   to   work 
under  a  constant  rate  of  production. 


Uniformity  of  conditions  should  prevail  as  to 
the  pressure  of  steam,  the  height  of  water,  the  rate 
of  evaporation,  the  thickness  of  fire,  the  times  of 
firing  and  quantity  of  coal  fired  at  one  time,  and  as 
to  the  intervals  between  the  times  of  cleaning  the 
fires. 

The  method  of  firing  to  be  carried  on  in  such  tests 
should  be  dictated  by  the  expert  or  person  in 
responsible  charge  of  the  test,  and  the  method 
adopted  should  be  adhered  to  by  the  fireman 
throughout  the  test. 

XIII.  Keeping  the  Records — Take  note  of 
every  event  connected  with  the  progress  of  the 
trial,  however  unimportant  it  may  appear.  Record 
the  time  of  every  occurrence  and  the  time  of 
taking  every  weight  and  every  observation. 

The  coal  should  be  weighed  and  delivered  to  the 
fireman  in  equal  proportions,  each  sufficient  for 
not  more  than  one  hour's  run,  and  a  fresh  portion 
should  not  be  delivered  until  the  previous  one  has 
all  been  fired.  The  time  required  to  consume  each 
portion  should  be  noted,  the  time  being  recorded 
at  the  instant  of  firing  the  last  of  each  portion.  It 
is  desirable  that  at  the  same  time  the  amount  of 
water  fed  into  the  boiler  should  be  accurately 
noted  and  recorded,  including  the  height  of  the 
water  in  the  boiler,  and  the  average  pressure  of 
steam  and  temperature  of  feed  during  the  time. 
By  thus  recording  the  amount  of  water  evaporated 
by  successive  portions  of  coal,  the  test  may  be 
divided  into  several  periods  if  desired,  and  the 
degree  of  uniformity  of  combustion,  evaporation, 
and  economy  analyzed  for  each  period.  In  ad- 
dition to  these  records  of  the  coal  and  the  feed 
water,  half  hourly  observations  should  be  made  of 
the  temperature  of  the  feed  water,  of  the  flue- 
gases,  of  the  external  air  in  the  boiler  room,  of  the 
temperature  of  the  furnace  when  a  furnace  pyro- 
meter is  used,  also  of  the  pressure  of  steam, 
and  of  the  readings  of  the  instruments  for  de- 
termining the  moisture  in  the  steam.  A  log 
should  be  kept  on  properly  prepared  blanks  con- 
taining columns  for  record  of  the  various  observa- 
tions. 

When  the  "standard  method"  of  starting  and 
stopping  the  test  is  used,  the  hourly  rate  of  com- 
bustion and  evaporation  and  the  horse-power 
should  be  computed  from  the  records  taken  during 
the  time  when  the  fires  are  in  active  condition. 
This  time  is  somewhat  less  than  the  actual  time 
which  elapses  between  the  beginning  and  end  of 
the  run.  The  loss  of  time  due  to  kindling  the  fire 


*The  gauge-glass  should  not  be  blown  out  within  an  hour  before  the  water  level  is  taken  at  the  beginning  and  end  of  test, 
otherwise  an  error  in  the  reading  of  the  water  level  may  be  caused  by  a  change  in  the  temperature  and  density  of  the  water  in 
the  pipe  leading  from  the  bottom  of  the  glass  into  the  boiler. 


204 


THE    STIRLING   WATER-TUBE   SAFETY  BOILER 


at  the  beginning  and  burning  it  out  at  the  end  makes 
this  course  necessary. 

XIV.  Quality  of    Steam  — The    percentage    of 
moisture  in  steam  should  be  determined  by  the  use 
of  either  a  throttling  or  a  separating   steam  calori- 
meter.*    The    sampling   nozzle    should   be    placed 
in  the  vertical  steam  pipe  rising  from   the    boiler. 
It  should  be  made  of  J-inch  pipe,  and  should  extend 
across   the   diameter  of  the   steam   pipe   to  within 
half  an  inch  of  the  opposite  side,  being  closed  at 
the  end  and  perforated  with  not  less  than  twenty 
J-inch  holes  equally  distributed  along  and  around 
its    cylindrical    surface,    but    none    of    these    holes 
should   be   nearer   than    J-inch    to    the   inner   side 
of    the    steam    pipe.     The    calorimeter    and    the 
pipe   leading   to   it   should   be   well   covered   with 
felting.     Whenever  the  indications  of  the  throttling 
or  separating  calorimeter  show  that  the  percentage 
of  moisture  is  irregular,  or  occasionally  in  excess 
of  three  per  cent.,  the  results  should  be  checked 
by  a  steam  separator  placed  in  the  steam  pipe  as 
close  to  the  boiler  as  convenient,  with  a  calorimeter 
in  the  steam  pipe  just  beyond  the  outlet  from  the 
separator.     The  drip  from  the  separator  should  be 
caught  and  weighed,  and  the  percentage  of  moisture 
computed  therefrom  added  to  that  shown  by  the 
calorimeter. 

Superheating  should  be  determined  by  means 
of  a  thermometer  placed  in  a  mercury-well  inserted 
in  the  steam  pipe.  The  degree  of  superheating 
should  be  taken  as  the  difference  between  the 
reading  of  the  thermometer  for  superheated  steam 
and  the  readings  of  the  same  thermometer  of 
saturated  steam  at  the  same  pressure  as  deter- 
mined by  a  special  experiment,  and  not  by  refer- 
ence to  steam  tables. 

For  calculations  relating  to,  and  corrections  for, 
quality  of  steam,  see  pages  79  to  85. 

XV.  Sampling  the  Coal  and   Determining  Its 
Moisture — As    each    barrow    load    or    fresh  por- 
tion of  coal  is  taken  from  the  coal  pile,  a  repre- 
sentative shovelful  is  selected  from  it  and  placed  in 
a  barrel  or  box  in  a  cool  place  and  kept  until  the  end 
of    the    trial.     The   samples    are    then    mixed   and 
broken  into  pieces  not  exceeding  one  inch  in  diam- 
eter,   and   reduced   by    the   processes    of   repeated 
quartering  and  crushing  until  a  final  sample  weigh- 
ing about  five  pounds  is  obtained,  and  the  size  of 
the  larger  piece  is  such  that  they  will  pass  through 
a   sieve   with    J-inch    meshes.     From    this    sample 
two  one-quart,   air-tight  glass  preserving  jars,   or 
other    air-tight    vessels    which    will    prevent    the 
escape   of   moisture   from    the    sample,    are    to   be 


promptly  filled,  and  these  samples  are  to  be  kept 
for  subsequent  determinations  of  moisture  and  of 
heating  value  and  for  chemical  analyses.  During 
the  process  of  quartering,  when  the  sample  has  been 
reduced  to  about  100  pounds,  a  quarter  to  a  half 
of  it  may  be  taken  for  an  approximate  determina- 
tion of  moisture.  This  may  be  made  by  placing 
it  in  a  shallow  iron  pan,  not  over  three  inches  deep, 
carefully  weighing  it,  and  setting  the  pan  in  the 
hottest  place  that  can  be  found  on  the  brickwork 
of  the  boiler  setting  or  flues  keeping  it  there  for 
at  least  1 2  hours,  and  then  weighing  it.  The  de- 
termination of  moisture  thus  made  is  believed  to  be 
approximately  accurate  for  anthracite  and  semi- 
bituminous  coals,  and  also  for  Pittsburg  or  Youghio- 
gheny  coal;  but  it  cannot  be  relied  upon  for  coals 
mined  west  of  Pittsburg,  or  for  other  coals  con- 
taining inherent  moisture.  For  these  latter  coals 
it  is  important  that  a  more  accurate  method  be 
adopted.  The  method  recommended  by  the  Com- 
mittee for  all  accurate  tests,  whatever  the  char- 
acter of  the  coal,  is  described  as  follows: 

Take  one  of  the  samples  contained  in  the  glass 
jars,  and  subject  it  to  a  thorough  air-drying,  by 
spreading  it  in  a  thin  layer  and  exposing  it  for 
several  hours  to  the  atmosphere  of  a  warm  room, 
weighing  it  before  and  after,  thereby  determining 
the  quantity  of  surface  moisture  it  contains.  Then 
crush  the  whole  of  it  by  running  it  through  an 
ordinary  coffee  mill  adjusted  so  as  to  produce  some- 
what coarse  grains  (less  than  i/i 6-inch),  thor- 
oughly mix  the  crushed  sample,  select  from  it  a 
portion  of  from  10  to  50  grams,  weigh  it  in  a  balance 
which  will  easily  show  a  variation  as  small  as  i 
part  in  1,000,  and  dry  it  in  an  air  or  sand  bath  at  a 
temperature  between  240  and  280  degrees  Fahr.  for 
one  hour.  Weigh  it  and  record  the  loss,  then  heat 
and  weigh  it  again  repeatedly,  at  intervals  of  an 
hour  or  less,  until  the  minimum  weight  has  been 
reached  and  the  weight  begins  to  increase  by  oxida- 
tion of  a  portion  of  the  coal.  The  difference  be- 
tween the  original  and  the  minimum  weight  is 
taken  as  the  moisture  in  the  air-dried  coal.  This 
moisture  test  should  preferably  be  made  on  dupli- 
cate samples,  and  the  results  should  agree  within 
0.3  to  0.4  of  one  per  cent.,  the  mean  of  the  two 
determinations  being  taken  as  the  correct  result. 
The  sum  of  the  percentage  of  moisture  thus  found 
and  the  percentage  of  surface  moisture  previously 
determined  is  the  total  moisture. 

XVI.  Treatment  of  Ashes  and  Refuse  — The 
ashes  and  refuse  are  to  be  weighed  in  a  dry  state.  If 
it  is  found  desirable  to  show  the  principal  character- 


*See  pages  79  to  83. 


THE    HEAT    BALANCE 


205 


istics  of  the  ash,  a  sample  should  be  subjected  to 
a  proximate  analysis  and  the  actual  amount  of  in- 
combustible material  determined.  For  elaborate 
trials  a  complete  analysis  of  the  ash  and  refuse 
should  be  made. 

XVII.  Calorific  Tests  and  Analysis  of    Coal— 
The  quantity  of  the  fuel  should  be  determined  either 
by  heat  test  or  by  analysis,  or  by  both. 

The  rational  method  of  determining  the  total 
heat  of  combustion  is  to  burn  the  sample  of  coal 
in  an  atmosphere  of  oxygen  gas,  the  coal  to  be 
sampled  as  directed  in  Article  XV  of  this  code. 

The  chemical  analysis  of  the  coal  should  be  made 
only  by  an  expert  chemist.  The  total  heat  of 
combustion  computed  from  the  results  of  the  ulti- 
mate analysis  may  be  obtained  by  the  use  of  Du- 
long's  formula,  pages  106  and  131. 

It  is  desirable  that  a  proximate  analysis  should 
be  made,  thereby  determining  the  relative  propor- 
tions of  volatile  matter  and  fixed  carbon.  These 
proportions  furnish  an  indication  of  the  leading 
characteristics  of  the  fuel,  and  serve  to  fix  the  class 
to  which  it  belongs.  As  an  additional  indication 
of  the  characteristics  of  the  fuel,  the  specific  gravity 
should  be  determined. 

XVIII.  Analysis  of  Flue=Gases  — The    analysis 
of  the  flue-gases  is  an  especially  valuable  method 
of    determining    the    relative    value    of    different 
methods  of  firing,  or  of  different  kinds  of  furnaces. 
In  making  these  analyses  great  care  should  be  taken 
to    procure    average    samples — since    the    composi- 
tion is  apt  to  vary  at  different  points  of  the  flue. 
The  composition  is  also  apt  to  vary  from  minute 
to  minute,  and  for  this  reason  the  drawings  of  gas 
should  last  a  considerable  period  of  time.     Where 
complete  determinations  are  desired,   the  analyses 
should   be   intrusted    to    an   expert   chemist.     For 
approximate    determinations    the    Orsat*    or    the 
Hempelf  apparatus  may  be  used  by  the  engineer. 

For  the  continuous  indication  of  the  amount  of 
carbonic  acid  (CO 2)  present  in  the  flue-gases,  an 
instrument  may  be  employed  which  shows  the 
weight  of  the  sample  of  gas  passing  through  it. 

XIX.  Smoke  Observations — It  is  desirable  to 
have  a  uniform  system  of  determining  and  record- 
ing   the    quantity    of    smoke    produced    where    bi- 
tuminous   coal    is    used.      The    system    commonly 
employed  is  to  express  the  degree  of  smokiness  by 
means    of    percentages    dependent    upon  the  judg- 
ment of  the  observer.     The  Committee   does  not 
place  much  value  upon  a  percentage  method,  be- 
cause   it    depends    so    largely    upon    the    personal 
element,  but  if  this  method  is  used,  it  is  desirable 


that,  so  far  as  possible,  a  definition  be  given  in 
explicit  terms  as  to  the  basis  and  method  employed 
in  arriving  at  the  percentage.  The  actual  meas- 
urement of  a  sample  of  soot  and  smoke  by  some 
form  of  meter  is  to  be  preferred. 

XX.  Miscellaneous — In   tests   for    purposes    of 
scientific  research,  in  which  the  determination  of 
all  the  variables  entering  into  the  test   is  desired 
certain    observations    should    be    made    which    are 
in  general  unnecessary  for  ordinary  tests.     These 
are  the  measurement  of  the  air  supply,  the  determi- 
nation of  its  contained  moisture,  the  determination 
of  the  amount  of  heat  lost  by  radiation,   of  the 
amount  of  infiltration  of  air  through  the  setting, 
and   (by  condensation  of  all  the  steam  made  by 
the  boiler)  of  the  total  heat  imparted  to  the  water. 

As  these  determinations  are  rarely  undertaken, 
it  is  not  deemed  advisable  to  give  directions  for 
making  them. 

XXI.  Calculations  of  Efficiency — Two  methods 
of  defining  and  calculating  the  efficiency  of  a  boiler 
are  recommended.     They  are: 

i.     Efficiency  of   the   boiler 

Heat  absorbed  per  Ib.  combustible 


Calorific  value  of  i  Ib.  combustible 
2 .     Efficiency  of  the  boiler  and  grate 
Heat  absorbed  per  Ib.  coal 


[52] 


Calorific  value  of  i  Ib.coal 
The  first  of  these  is  sometimes  called  the  effi- 
ciency based  on  combustible,  and  the  second  effi- 
ciency based  on  coal.  The  first  is  recommended 
as  a  standard  of  comparison  for  all  tests,  and  this 
is  the  one  which  is  understood  to  be  referred  to 
when  the  word  "efficiency"  alone  is  used  without 
qualification.  The  second,  however,  should  be  in- 
cluded in  a  report  of  a  test,  together  with  the  first, 
whenever  the  object  of  the  test  is  to  determine  the- 
efficiency  of  the  boiler  and  furnace  together  with 
the  grate  (or  mechanical  stoker),  or  to  compare 
different  furnaces,  grates,  fuels,  or  methods  of  firing. 
The  heat  absorbed  per  pound  of  combustible 
(or  per  pound  of  coal)  is  to  be  calculated  by  multi- 
plying the  equivalent  evaporation  from  and  at 
212  degrees  per  pound  combustible  (or  coal)  by 

965-74 

XXII.  The  Heat  Balance — An  approximate 
"heat  balance,"  or  statement  of  the  distribution 
of  the  heating  value  of  the  coal  among  the  several 
items  of  heat  utilized  and  heat  lost  may  be  included 
in  the  report  of  a  test  when  analyses  of  the  fuel 
and  of  the  chimney-gases  have  been  made.  The 
methods  of  computing  the  heat  balance  and  the 


*See  page  184.     tSee  Hempel's  Methods  of  Gas  Analysis.     (Macmillan  &  Co.)     £965. 8  is   more  accurate,  and  is  used  through- 
out this  book. 


206 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


form  in  which  it  should  be  reported,  are  given  in       12.  Draft  between  damper  and  boiler ins.  of  water 

chapter  on  Steam  Boiler  Efficiency.  13.  Force  of  draft  in  furnace " 

XXIII.      Report    of   the   Trial— The    data    and       14.  Force  of  draft  or  blast  in  ash-pit.... 
results  should  be  reported  in  the  manner  given  in  Average  Temperatures. 

either  one    of    the  two  following    tables,"!"  omitting       15.  Of  external  air deg. 

lines  where  the  tests  have  not  been  made  as  elabor-       16.  Of  fireroom  " 

ately  as  provided  for  in  such  tables.     Additional       17.  Of  steam  

lines  may  be  added  for  data  relating  to  the  specific       18.  Of  feed  water  entering  heater " 

object    of    the    test.     The    extra    lines    should    be       19.  Of  feed  water  entering  economizer " 

classified  under  the  headings  provided  in  the  tables,       20.  Of  feed  water  entering  boiler  " 

and  numbered  as  per  preceding  line,  with  sub-letters      21.  Of  escaping  gases  from  boiler " 

a,   b,   etc.     The  Short  Form  of  Report  is  recom-       22.  Of  escaping  gases  from  economizer  " 

mended  for  commercial  tests  and  as  a  convenient  Fuel. 

form  of  abridging  the  longer  form  for  publication       23.  Size  and  condition  

when  saving  of  space  is  desirable.      For  elaborate       24.  Weight  of  wood  used  in  lighting  fire Ibs. 

trials,  it  is  recommended  that  the  full  log  of  the       25.  Weight  of  coal  as  fired*    _ " 

trial  be  shown  graphically,  by  means  of  a  chart.       26.  Percentage  of  moisture  in  coal% percent. 

27.  Total  weight  of  dry  coal  consumed 

DATA     AND     RESULTS     OF     EVAPORATIVE       28.  Total  ash  and  refuse 

TgST  29.  Quality  of  ash  and  refuse 

30.  Total  combustible  consumed ....  ..Ibs. 

Arranged  in  accordance  with  the  Complete  Form,  ,-.  ,        ,  .        ,          .        . 

31.  Percentage    of   ash     and    refuse   in    dry    coal 
Code  of  1899. 

per  cent. 

Made  by ot boiler  at to  ,-,  .,,..„. 

Proxtmate  Analysis  of  Coal. 

determine.. 

Coal.     Combustible. 
Principal  conditions  governing  the  trial .... 

32.  Fixed  carbon per  cent,     per  cent. 

33.  Volatile  matter 

Kind  of  fuel ...  .  ^ 

„.    ,    ,  ,  34-  Moisture... 

Kind  of  furnace  ..  ,, 

State  of  the  weather _ 

Method  of  starting  and  stopping  the  test  ("stand- 

dard"  or  "alternate,"  Art.  X  and  XI,  Code)....  36.  Sulphur,     separately    de- 

1 .  Date  of  trial termined  .. 

2.  Duration  of  trial   ..  ....hours.  Ultimate  Analysis  of  Dry  Coal. 

Dimensions  and  Proportions .  (Art.  XVII.,  Code.) 

(A  complete  description  of  the  boiler,  and  draw-  Coal.      Combustible, 

ings  of  the  same  if  of  unusual  type,  should  be  given      37-  Carbon  (C)  ....percent,     percent, 

on  an  annexed  sheet.)  38.  Hydrogen  (H) 

3.  Grate   surface width  length      39-  Oxygen  (O)  ... 

....area....  ..  sq.  ft.      40.  Nitrogen  (N)    . 

4.  Height  of  furnace  ..  ....ins.       4i-  Sulphur  (S)  ... 

5.  Approximate  width  of  air  spaces  in  grate....     in.       42-  Ash    . 

6.  Proportion   of  air   space    to   whole   grate   sur-  100  %  100  % 

face _ percent.      43.  Moisture  in  sample  of  coal 

7.  Water-heating  surface sq.ft.  as  received 

8.  Superheating  surface Analysis   of   Ash   and   Refuse. 

9.  Ratio   of  water-heating  surface   to   grate   sur-      44.  Carbon    . per  cent. 

face....  — to  i.      45.  Earthy  matter. 

10.  Ratio  of  minimum  draft  area  to  grate  sur-  Fuel  per  Hour. 

face i  to .      46.  Dry  coal  consumed  per  hour  Ibs. 

Average  Pressures.  47.  Combustible  consumed  per  hour  . 

11.  Steam  pressure  by  gauge ...Ibs.  persq.  in.      48.  Dry  coal  per  sq.  ft.  of  grate  surface  per  hour  " 

tTo  save  space,  only  the  table  giving  the  "Complete  Form"  is  here  reproduced,  but  the  items   printed  in    italics  constitute  the 

"Short  Form."  *Including  equivalent  of  wood  used  in  lighting  the  fire,  not  including  unburnt  coal  withdrawn  from  furnace 
at  times  of  cleaning  and  at  end  of  test.  One  pound  of  wood  is  taken  to  be  equal  to  0.4  pounds  of  coal,  or,  in  'case  greater 
accuracy  is  desired,  as  having  a  heat  value  equivalent  to  the  evaporation  of  6  pounds  of  water  from  and  at  212  degrees  per  pound. 
(For  more  complete  information  on  this  point  see  page  up.)  The  term  "as  fired"  means  in  its  actual  condition,  including  moist- 
ure. tThis  is  the  total  moisture  in  the  coal  as  found  by  drying  it  artificially,  as  described  in  Art.  XV.  of  Code. 


207 


49-     Combustible  per  square  foot  of  water  heat- 
ing surface  per  hour Ibs. 

Calorific  Value  of  Fuel. 
(Art.  XVII.,  Code.) 

50.  Calorific  value  by  oxygen  calorimeter, 

perlb.  of  dry  coal B.  T.  U. 

51.  Calorific  value  by   oxygen  calorimeter, 

per  Ib.  of  combustible " 

52.  Calorific  value  by  analysis,  per  Ib.  of 

dry    coal*    " 

53.  Calorific  value  by  analysis,  per  Ib.  of 

combustible   

Quality  of  Steam. 

54.  Percentage  of  moisture  in  steam ..per  cent. 

55.  Number  of  degrees  of  superheating deg. 

56.  Quality  of  steam  (dry  steam= unity)     

Water. 

57.  Total  weight  of  water  fed  to  boiler^ Ibs. 

58.  Equivalent  water  fed  to  boiler  from  and  at 

212  degrees  " 

59.  Water    actually    evaporated,    corrected    for 

quality  of  steam " 

60.  Factor    of   evaporation!  " 

61.  Equivalent    water    evaporated    into    dry 

steam    from    and    at    212    degrees! 

(Item  5(;X  Item  60.)     " 

Water  per  Hour. 

62.  Water   evaporated   per   hour,   corrected  for 

quality  of  steam " 

63.  Equivalent  evaporation  per  hour  from  and 

at    212   degrees^ " 

64.  Equivalent  evaporation  per  hour  from  and 

at  212  degrees  per  square  foot  of    water 
heating  surface^ " 

Horse-Power. 

65.  Horse-Power  developed  (34$  Ibs.  of  water 

evaporated  per  hour  into  dry  steam  from 
and  at  212  degrees,  equals  one  horse- 
power^      .  H.  P. 

66.  Builders'  rated  horse-power " 

67.  Percentage  of  builders'  rated  horse-power 

developed per     cent. 

Economic  Results. 

68.  Water  apparently  evaporated  under  actual 

conditions   per   pound   of   coal   as   fired. 
(Item  si+Item  25.) Ibs. 

69.  Equivalent   evaporation   from    and    at    212 

degrees  per  pound  of  coal  as  fired\. 
(Item  6i-i-Item  25.) " 


70.  Equivalent  evaporation  from  and  at  212  de- 

grees per  pound  of  dry  coal\.  (Item 
6i-^-Item  27.) Ibs. 

7 1 .  Equivalent   evaporation   from   and   at    212 

degrees      per     pound     of     combustible^ 

(Item  6i+Item  30.) " 

(If  the  equivalent  evaporation,  Items 
69,  70  and  71,  is  not  corrected  for  the 
quality  of  steam,  the  fact  should  be 
stated.) 

Efficiency. 
(Art.  XXI,  Code.) 

7  2 .  Efficiency  of  boiler;  heat  absorbed  by  the  boiler 
per  Ib.  of  combustible  divided  by  the  heat  value 
of  one  Ib.  of  combustible]]  percent. 

73.  Efficiency  of   boiler,    including   the  grate;   heat 

absorbed  by  the  boiler,  per  Ib.  of  dry  coal, 
divided  by  the  heat  value  of  one  Ib.  of  dry 
coal per  cent. 

Cost  of  Evaporation. 

74.  Cost  of  coal  per  ton  of Ibs.   delivered  in 

boiler  room $ 

75.  Cost  of  fuel  for  evaporating  1,000  Ibs  of 

water  under  observed  conditions $ 

76.  Cost  of  fuel  used  for  evaporating  1,000  Ibs 

water  from  and  at  212  degrees ...$ 

Smoke  Observations. 

77.  Percentage  of  smoke  as.observed per  cent. 

78.  Weight    of    soot    per    hour    obtained 

from  smoke  meter ounces. 

79.  Volume    of   soot   per    hour   obtained 

from  smoke  meter  cub.  in. 

Methods  of  Firing. 

80.  Kind  of  firing   (spreading,   alternate 

or  coking).... 

81.  Average  thickness  of  fire 

82.  Average  intervals  between  firing  for 

each   furnace    during    time    when 
fires  are  in  normal  condition 

83.  Average    interval    between    times    of 

leveling  or  breaking  up... 

Analyses  of  the  Dry  Gases. 

84.  Carbon  dioxide  (CO.;) .per  cent. 

85.  Oxygen  (O)    ....".. " 

86.  Carbon  monoxide  (CO) 

87.  Hydrogen  and  hydrocarbons 

88.  Nitrogen  (by  difference)  (N) 


100  per  cent 


*See  Formula  No.  24,  page  106.         tCorrected  for  inequality  of  water  level  and  of  steam  pressure  at  beginning  and  end  of  test. 

t  Factor  of  evaporation,  see  page  70.  JThe  symbol  "U.  E."  meaning  "Units  of  Evaporation,"  may  be  conveniently 
substituted  for  the  expression  "Equivalent  water  evaporated  into  dry  steam  from  and  at  212  degrees,"  its  definition  being  given 
in  afoot-note.  See  page  72.  §Held  to  be  the  equivalent  of  30  Ibs.  of  water  per  hour  evaporated  from  100  degrees  Fahr.  into 
dry  steam  at  70  Ibs.  gauge  pressure.  See  page  195.  Illn  all  eases  where  the  word  combustible  is  used,  it  means  the  coal 

without  moisture  and  ash  but  including  all  other  constituents.  It  is  the  same  as  what  is  called  in  Europe  "coal  dry  and  free 
from  ash."  See  foot-note  on  page  112. 


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Mergenthaler  Linotype  Co.  Brooklyn 
Mergenthaler  Linotype  Co.,  Brooklyn 

Midvale  Colliery,  Wilburton,  Pa  . 
Lehigh  &  Wilkes-Barre  Coal  Co. 
Lehigh  ct  Wilkes-Barre  Coal  Co. 

Blackstone  Mfg.  Co.,  Blackstono,  Ma~ 
Toledo  Water  Works.,  Toledo,  O. 

Portland  (Me.)  Street  Railway  Co. 
Public  Works.  ,  Bangor,  Me. 

Old  Colony  S  reet  Ry.  Co.,  Taunton,  I 
Winilber  Electric  Co.,  Windber,  Pa. 

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Boilers  for  Mining  Service 


To  prove  satisfactory  for  mining  service 
a  boiler  must  be  capable  of  meeting  a  wider 
range  of  requirements  than  is  ordinarily 
met  with  in  other  industries.  It  must  be 
simple  in  construction  so  that  repairs  can  be 
quickly  made  with  the  limited  equipment 
usually  available;  it  must  be  safe  in  opera- 
tion because  skilled  boiler  attendants  are 
often  unavailable;  it  must  be  easy  to  force 
in  emergencies,  and  its  design  of  fire-box 
must  be  such  as  to  permit  use  of  wood,  oil, 
and  high  or  low  grade  coal.  The  boiler 
must  be  reasonable  in  first  cost,  because  of 
the  uncertainty  as  to  the  life  of  many  mines, 
and  it  must  also  be  easy  to  transport  into 
places  difficult  of  access.  An  especially 
important  requirement  is  that  the  boiler  can 
be  opened,  cleaned  and  closed  in  the  shortest 
possible  time,  not  only  because  of  the  ex- 
pense of  keeping  it  out  of  commission,  but 
because  of  the  high  cost  of  labor.  The  single 
item  of  labor-cost  of  cleaning  some  types 
of  boilers  has  prevented  their  extensive  use 
for  mining  plants. 

A  careful  reading  of  the  preceding  descrip- 
tion of  the  Stirling  boiler  will  demonstrate 
that  it  perfectly  meets  each  of  these  re- 
quirements, and  surpasses  any  competing 
type  in  its  adaptation  to  varying  fuel  re- 
quirements, and  ease  and  cheapness  of  cleaning. 
A  more  convincing  evidence  that  it  is  justly 
regarded  as  the  "Ideal  Boiler  for  Mine  Use" 
is  found  in  the  fact  that  over  200,000  horse- 
power of  Stirling  boilers  are  now  in  success- 
ful operation  in  mine  and  smelter  plants. 

Boilers  supplying  Hoisting  Engines  are 
often  blamed  for  insufficient  capacity,  wet 
steam,  etc.,  when  the  fault  is  due  not  to 
the  boiler,  but  to  improper  piping.  The 
hoist  is  usually  some  distance  from  the 
boiler,  and  often  the  steam  pipe  is  so  imper- 
fectly covered  that  between  lifts  large  quan- 
tities of  steam  condense  and  the  water  thus 
formed  is  swept  into  the  cylinder  when  the 
engine  starts.  When  the  throttle  is  thrown 
open  the  momentary  draft  on  the  boiler  may 
be  many  times  greater  than  its  rated  capacity 
and  in  such  cases,  irrespective  of  the  kind  of 
boiler,  there  may  be  a  momentary  lift  of 


water.  To  prevent  this  it  is  common  prac- 
tise to  provide  the  boiler  with  an  auxiliary 
steam  drum,  but  this  is  a  makeshift  and  not 
a  cure,  as  will  now  be  shown. 

Condensation  in  the  pipe  line  cannot  be 
prevented,  but  it  can  be  largely  reduced, 
and  the  evident  means  are  an  efficient  cover- 
ing of  ample  thickness,  and  a  reduction  of 
the  capacity.  A  reliable  method  of  extracting 
all  water  of  condensation  before  the  steam 
enters  the  engine  is  necessary. 

Consider  the  case  of  a  tank  supplied  with 
water  through  a  pipe  connected  to  a  distant 
reservoir.  It  is  evident  that  if  one  wants 
to  fill  the  tank  say  every  minute,  yet  allow 
only  one-quarter  of  a  minute  to  do  the  .actual 
filling,  and  shut  off  the  pipe  the  other  three- 
quarters  of  a  minute,  then  the  column  of 
water  in  the  pipe  is  not  only  started  and 
stopped  at  every  filling,  but  the  capacity 
of  the  pipe  will  have  to  be  four  times  as 
great  as  would  be  the  case  if  the  water  ran 
all  the  time  into  a  storage  tank  from  which 
the  other  tank  could  be  filled  at  the  same 
intervals  as  before.  Provided  the  original 
reservoir  feeding  the  pipe  were  of  sufficient 
size  to  supply  the  requisite  volume  of  water, 
any  further  increase  in  its  size  could  not 
alter  in  the  slightest  degree  the  action  as 
above  described. 

If  in  the  above  case  a  boiler  be  substituted 
for  the  reservoir,  and  a  hoisting  engine  for 
the  tank  to  be  periodically  filled,  then  the 
storage  tank  from  which  it  is  to  be  filled 
corresponds  exactly  to  the  steam  drum, 
hence  it  is  evident  that  when  the  drum  is 
placed  on  the  boiler,  it  is  at  the  wrong  end 
of  the  line.  Its  proper  place  is  as  near  to 
the  engine  as  it  can  possibly  be  put,  and  its 
cubical  capacity  should  be  not  less  than 
one-seventh  the  actual  volume  of  steam  used 
per  minute  by  the  engine.  It  should  be 
well  covered,  and  provided  with  an  absolutely 
reliable  drainage  apparatus,  and  a  gauge  glass 
to  indicate  when  that  apparatus  fails  to 
work.  Steam  traps  are  not  always  reliable, 
and  an  automatic  drainage  pump  is  better. 

The  area  of  the  steam  pipe  may  next  be 
figured.  The  maximum  number  of  strokes 


SIZE    OF    STEAM    PIPE    FOR    HOISTING    ENGINES 


211 


per  minute  of  the  engine  being  known,  dis- 
regard the  cut-off  and  assume  the  cylinder 
is  entirely  filled  with  steam  at  each  stroke, 
then  compute  the  diameter  of  steam  pipe 
between  engine  and  drum  based  on  steam 
velocity  of  6,000  feet  per  minute.  This 
velocity  will  actually  exist  during  the  part 
of  the  stroke  up  to  cut-off,  since  the  velocity 
of  the  steam  at  that  time  will  be  the  same 
as  it  would  be  were  the  engine  taking  steam 
during:  the  entire  stroke. 


flow  in  the  engine  supply  pipe  will  continue 
only  up  to  time  the  engine  cuts  off ;  the  steam 
being  elastic  and  the  drum  acting  as  a  re- 
ceiver and  pressure  steadier  (like  the  rubber 
bag  in  a  gas  engine  supply  pipe)  the  flow  of 
steam  between  boiler  and  drum  will  be 
practically  continuous,  hence  its  velocity 
will  be  less  than  assumed  in  the  calculation. 
The  decrease  in  pipe  size  will  reduce  the 
surface  available  for  condensation.  The  stor- 
age drum  next  to  the  engine  is  preferably 


LOS   ANGELES-PACIFIC    RAILROAD,   LOS   ANGELES,  CAL.  OPERATING    1,300    H.  P.  OF  STIRLING    BOILERS 


To  reduce  the  condensation,  the  pipe  be- 
tween boiler  and  drum  should  be  no  larger 
than  actually  required,  and  it  will  be  en- 
tirely safe  to  figure  its  area  in  exactly  the 
same  manner  as  above  shown  for  engine 
supply  pipe,  except  that  the  steam  velocity 
may  be  assumed  as  8,000  or  even  9,000  feet 
per  minute.  The  actual  velocity  through  the 
pipe  thus  determined  will  be  less  than  these 
figures,  because  the  volume  of  steam  as- 
sumed as  basis  of  the  calculation  is  that  which 
would  be  required  to  fill  the  entire  engine 
cylinder  if  there  were  no  cut-off;  actually  the 


made  vertical,  and  to  assist  in  separating 
any  water  a  vertical  partition  should  extend 
from  the  top  to  within  18  inches  of  the 
bottom,  and  both  steam  inlet  and  outlet 
should  be  near  the  top.  To  secure  the  maxi- 
mum of  volume  with  minimum  of  exposed 
surface,  the  diameter  and  length  should  not 
differ  greatly. 

Regardless  of  the  purpose  for  which  a 
steam  plant  may  be  used,  there  are  many 
more  cases  than  commonly  supposed  where 
an  arrangement  of  drum  and  piping  as  above 
described  would  be  a  profitable  investment. 


PART   OF    11    600    H     P.    OF   STIRLING    BOILERS,   WASHOE   SMELTER,    ANACONDA   COPPER    MINING   CO. 

ANACONDA,    MONTANA 


Principles  of  Steam  Piping 


In  the  design  of  a  steam  plant  no  detail 
merits  more  careful  consideration  than  the 
steam  piping.  Not  only  is  it  frequently 
overlooked,  but  the  evils  resulting  from  de- 
fective design  are  usually  attributed  to  other 
parts  of  the  equipment. 

The  nature  of  the  material  to  be  conveyed 
by  the  pipe  must  be  considered,  as  the  re- 
quirements for  steam  are  entirely  different 
from  those  of  water,  oil,  or  gas.  The  princi- 


ample  strength,  provision  for  expansion, 
and  valves  of  suitable  type  properly  located. 
No  perfect  heat  insulator  is  known ;  the 
loss  of  heat  from  steam  pipes  by  radiation 
may  be  reduced  by  methods  given  in  the 
next  chapter,  but  it  cannot  be  wholly  pre- 
vented, hence  some  water  of  condensation 
must  form.  If  this  water  as  fast  as  it  is 
formed  is  carried  to  the  engine  it  will  cause 
troubles  which  will  later  be  pointed  out.  If 


TABLE  61 

STANDARD  DIMENSIONS  OF  WROUGHT  IRON  AND  STEEL   STEAM,  GAS 

AND    WATER   PIPE* 


Diameter. 

Circumference. 

Transverse  Areas. 

Length  of  Pipe  per 
Square  Foot  of 

Length 

v  % 

C  ^ 

of  Pipe 

jlJSl 

Contain- 

Nominal 

£   , 

11 

11 

Actual 
External 

Approxi- 
mate 
Internal 

l| 

External. 

Internal. 

External. 

Internal. 

Metal. 

External 
Surface. 

Internal 
Surface. 

ing  one 
Cubic 
Foot. 

Weight 
per 
Foot. 

•s"3 

~    o 

Diameter 

Diameter 

-Q  C 

Inch. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Sq.  Inch. 

Sq.  Inch. 

Sq.  Inch. 

Feet. 

Feet. 

Feet. 

Pounds. 

£! 

, 

-405 

.27 

068 

1.272 

.848 

.  129 

-0573 

.0717 

9-44 

14-  15 

2513- 

.  241 

2-7 

1 

-54 

•  364 

088 

i  .'696 

1.  144 

.  229 

.1041 

•  1249 

7-075 

10.49 

1383-3 

.42 

18 

1 

.675 

•494 

091 

2  .  121 

1-552 

-358 

•  1917 

.1663 

5-657 

7-73 

751  -2 

-559 

18 

.84 

.623 

109 

2.639 

1-957 

•  554 

.3048 

•  2492 

4-547 

6.13 

472.4 

-837 

14 

J 

1.05 

.824 

113 

3.299 

2.589 

.866 

-5333 

•  3327 

3.637 

4-635 

270. 

1.115 

14 

i 

I.3I5 

i  .048 

i34 

4-131 

3.292 

1.358 

.8626 

•  4954 

2.904 

3-645 

166.  9 

1.668 

ii* 

ii 

1.66 

1.38 

14 

5-215 

4-335 

2.  164 

i  .496 

•     .668 

2  .301 

2.768 

96.25 

2.244 

ii* 

i* 

1.9 

i  .61  1 

i45 

5-969 

5.061 

2.835 

2.038 

-797 

2  .OI 

2.371 

70  .66 

2.678 

ii* 

2 

2.375 

2  .067 

i54 

7-461 

6-494 

4-43 

3-356 

1.074 

I  .608 

1.848 

42.91 

3-609 

1  1* 

2* 

2.875 

2.468 

204 

9.032 

7-753 

6.492 

4.784 

1.708 

1.328 

i  -547 

30.  i 

5-739 

8 

3 

3-5 

3.067 

217 

10.  996 

9  .  636 

9.621 

7  .  388 

2.243 

I  .09! 

i  .  245 

19.5 

7.536 

8 

3* 

4- 

3.548 

226 

12  .  566 

ii  .  146 

12.566 

9  .  887 

2.679 

-955 

1.077 

14-57 

9  .001 

8 

4 

4-5 

4  .026 

237 

14.137 

I  2  .  648 

15.904 

12.73 

3-174 

-849 

•949 

11.31 

10  .  665 

8 

4* 

5- 

4.5o8 

246 

15.708 

14.  l62 

I9-635 

15.961 

3-674 

•  764 

.848 

9  .02 

12.49 

8 

5 

5-563 

5-045 

259 

17-477 

15.849 

24.306 

19.  qp 

.687 

•757 

7.2 

14.502 

8 

6 

6.  625 

6.065 

28 

2O.8l3 

I9.O54 

34-472 

28.888 

5  '584 

-577 

•  63 

4.98 

18.762 

8 

7 

7-625 

7.023 

301 

23-9.55 

22.063 

45.664 

38.738 

6  .  926 

.501 

-544 

3.72 

23-271 

8 

8 

8.625 

7.982 

322 

27  .096 

25.076 

58.426 

50.04 

8.386 

-443 

.478 

2.88 

28.177 

8 

9 

9.625 

8.937 

344 

30.238 

28.076 

72.76 

62.73 

10.03 

-397 

.427 

2.29 

33-701 

8 

10 

10.75 

10.019 

366 

33-772 

31-477 

90.763 

78.839 

11.924 

•  355 

.382 

1.82 

40  .065 

8 

1  1 

11-75 

1  1  . 

36.914 

34.558 

108.434 

95-033 

13.401 

-325 

•  347 

1.51 

45  .028 

8 

I  2 

12.75 

I  2  . 

40.055 

37-7 

127  .677 

113  .098 

I4-S79 

.  290 

-319 

i  .  27 

48.985 

8 

pies  governing  steam  pipe  design  are:  (i) 
The  moment  steam  leaves  the  boiler  it  loses 
heat  and  some  of  it  must  condense.  (2) 
Water  of  condensation  is  an  evil,  and  since 
its  formation  cannot  be  wholly  prevented 
a  perfect  pipe  system  must  provide  means 
of  removing  it  as  fast  as  it  forms.  (3)  There 
can  be  no  flow  of  steam  without  a  correspond- 
ing drop  of  pressure.  (4)  Drop  of  pres- 
sure of  steam  does  not  cause  a  loss  of  energy. 
(5)  The  mechanical  design  must  provide 

*From  Crane  Company's  Catalog. 


the  pipe  contains  low  spots  or  "pockets" 
where  the  water  can  accumulate  it  will 
gradually  decrease  the  effective  pipe  area 
until  the  steam  velocity  is  increased  to  a 
sufficient  degree  to  lift  the  water  and  sweep 
it  along  the  pipe.  This  is  especially  liable 
to  happen  when  the  demand  for  steam  is 
irregular;  when  the  flow  is  small  the  water 
will  settle  into  the  pockets  but  when  the 
heavy  load  is  suddenly  thrown  on,  the  re- 
sulting rush  of  steam  will  carry  the  water 


214 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


bodily  with  it.  Since  water  is  practically 
incompressible  its  effect  when  traveling  at 
high  velocity  differs  little  from  that  of  a 
solid  body  of  equal  weight,  hence  its  impact 
agrinst  elbows,  valves,  or  other  obstructions, 
is  equivalent  to  a  heavy  hammer  blow,  and 
frequently  the  pipe  is  ruptured.  If  the  quan- 
tity of  water  is  insufficient  to  produce  such 
serious  results,  it  will  certainly  cause  knock- 
ing and  vibrations  in  the  pipes,  the  final 
consequence  of  which  will  be  leaky  joints. 
When  the  water  reaches  the  engine  its  effects 
will  vary  from  disagreeable  knocking  to 
destruction  of  the  engine.  In  such  cases  the 
usual  procedure  is  to  blame  the  boiler  for 
producing  "wet"  steam,  but  the  fallacy  of 
this  view  can  easily  be  shown.  Assume  a 
compound  condensing  engine  which  develops 
200  H.  P.  under  125  Ibs.  gauge  pressure,  and 


pies  governing  this  removal.  Each  sketch 
represents  an  elevation  of  a  system  of  steam 
piping. 

M  indicates  the  boiler  and  E  the  engines. 
Sketch  .1  shows  the  simplest  scheme  of  pip- 
ing. All  the  water  of  condensation  will 
flow  into  the  engines,  unless  removed  by 
separators  at  5.  If  all  the  engines  are  shut 
down,  water  will  collect  in  the  pipes,  and 
unless  it  be  drained  off  by  "bleeders"  it  will 
cause  trouble  when  an  engine  is  started. 

In  sketch  B  the  engine  connections  are 
taken  from  the  top  of  the  main,  hence  most 
of  the  water  will  flow  to  the  "dead  end"  or 
drop  leg  X;  the  small  amount  carried  over 
to  the  5ngine  may  be  removed  by  the  sepa- 
rators 5.  The  water  which  collects  at  A' 
must  be  continuously  removed  by  a  trap  or 
pump,  and  if  this  be  done  the  system  will 


f 

( 

\    j 

~N 

^       r 

s 

L 

X 

< 

's   J 

s 

h       r^ 

5 

I 

•1 

[_ 

LI      Li 

J       LJ 

LJ 

r 

4 

[j 

y       [_ 

y        [E 

J 

A 

B 

FIG.  43.     LINE    DIAGRAMS   SHOWING    ELEVATION    OF  STEAM    PIPE   SYSTEMS 


uses  1 8  Ibs.  of  steam  per  horse-power  hour. 
Assume  that  the  air  temperature  is  80°, 
and  that  the  steam  pipe  is  6  inches  dia.,  and 
150  feet  long.  The  engine  will  use  3,600  Ibs. 
of  steam  per  hour,  and  under  the  given  con- 
ditions the  steam  pipe,  if  uncovered,  will 
condense  about  225  Ibs.  per  hour,  or  6.25% 
of  the  total.  If  by  proper  covering  80% 
of  this  condensation  can  be  prevented,  the 
remainder  will  be  i.25%of  the  total,  and 
the  boiler  is  in  no  sense  responsible  for  this 
amount  of  moisture  in  the  steam.  In  many 
cases  where  properly  designed  boilers  are 
blamed  for  wet  steam,  a  similar  analysis 
would  locate  the  trouble  in  the  steam  pipes. 
Removal  of  the  Water — It  follows  that 
efficient  means  of  removing  the  water  of 
condensation  are  absolutely  imperative.  The 
sketches  in  Fig.  43  will  illustrate  the  princi- 


be  drained,  and  the  piping  maintained  at  an 
even  temperature,  whether  the  engines  are 
operating  or  not. 

If  the  trap  or  pump  at  X  be  replaced  by  a 
drain  pipe  which  is  connected  below  the 
boiler  water-line,  as  in  sketch  C,  the  steam 
main  is  at  once  converted  into  a  high  pres- 
sure gravity  steam-Heating  system,  and  it  will 
automatically  drain  itself,  provided  the  drop 
in  pressure  in  the  main  is  not  sufficient  to 
maintain  a  level  \)t  water  in  the  drain  higher 
than  the  point  X.  If  the  level  due  to  the 
drop  be  lower  than  the  separators  5,  then 
their  drips  also  could  be  connected  to  the 
drainage  pipe,  and  in  that  case  the  engine 
supply  pipes  will  form  part  of  the  high  pres- 
sure heating  system,  and  will  be  self  draining. 
Should  it  be  necessary  to  make  a  dip  or  pocket 
in  the  steam  main,  as  at  Y,  its  lowest  point 


ADVANTAGES    OF    AN    EFFICIENT    DRAINAGE   SYSTEM 


215 


should  also  be  connected  to  the  drainage 
system.  Thus  arranged,  the  entire  system 
will  maintain  its  circulation,  there  will  be 
no  straining  due  to  heating  and  cooling, 
and  the  system  will  be  self-draining  whether 
the  engines  be  working  or  not.  All  such 
drainage  connections  should  be  provided 
with  check  valves,  as  shown  in  Fig  44. 

When  boilers  are  situated  a  sufficient  dis- 
tance below  the  engines  (as  in  some  mills), 
the  installation  of  piping  arranged  as  a 
gravity-return  system  is  entirely  feasible 
and  the  results  leave  nothing  to  be  desired. 
In  most  cases  the  necessary  difference  of 
level  cannot  be  obtained,  and  a  mechanical 
equivalent  for  it  must  be  installed.  The 
usual  method  is  to  install  either  steam  traps, 
which  will  deliver  the  water  of  condensation 
into  the  heater  or  hot  well;  or  steam  pumps, 
which  will  return  the  water  directly  into  the 
boiler  at  practically  steam  temperature.  A 
number  of  drain  pipes  are  connected  to  each 
trap  or  pump.  Traps  are  not  as  reliable  as 
pumps,  hence  the  latter  should  be  preferred 
if  the  amount  of  work  to  be  done  will  justify 
their  greater  cost. 

Branches  from  the  mains  should  never 
be  taken  from  the  bottom.  When  possible 
they  should  be  taken  from  the  top,  and  a 
horizontal  partition  in  the  center  of  the 
tee  will  still  further  improve  the  action, 
since  in  case  of  a  sudden  demand  for  steam 
at  the  engine,  the  water  flowing  along  the 
bottom  of  the  main  cannot  be  lifted  into  the 
outlet  pipe. 

The  pitch  of  all  pipe  should  be  in  the  direc- 
tion of  the  steam  travel.  Whenever  a  rise 
in  the  main  is  necessary,  a  drain,  as  at  Y  in 
sketch  C,  should  be  tapped  into  the  lowest 
point  just  below  the  rise.  The  mains  and 
all  important  branches  should  terminate  in  a 
drop-leg,  as  at  X,  and  every  such  drop-leg 
or  other  low  spot  in  the  system,  should  be 
connected  to  the  drainage  pump.  A  similar 
connection  should  be  made  to  every  fitting 
which  is  of  such  shape  that  it  can  form  a 
water  pocket.  An  effective  method  of  drain- 
ing the  mains  is  to  run  at  a  suitable  distance 
below  them  a  small  drainage  pipe,  about  i^ 
to  i^-inch  dia.,  which  is  connected  to  all 
low  spots  in  the  piping  or  fittings,  and  con- 
veys the  water  to  the  drainage  pump.  To 
prevent  this  pipe  from  delivering  steam  and 


water  into  any  section  of  the  main  from  which 
steam  mav  have  been  cut  off  bv  the  regular 
valve  systems,  a  swinging  check  valve  should 
be  inserted  into  each  connection  between 
the  main  and  the  drainage  pipe.  This  valve 
can  be  placed  at  an  angle  of  nearly  45°,  as 
in  Fig.  44,  so  that  the  check  valve  disk 
is  nearly  vertical,  hence  requires  practically 
no  head  of  water  to  open  it  when  in  action. 
Each  engine  supply  pipe  should  have  its 
own  separator  placed  as  near  the  throttle 
as  possible,  and  the  drains  from  these  sep- 
arators can  be  connected  to  a  drainage 
system  also. 


FIG.  44.    LOCATION  OF  CHECK  VALVE  IN  DRAIN  PIPE 

Drain  pipes  which  are  occasionally  opened 
by  hand  may  be  useful  for  blowing  out  large 
quantities  of  water  at  intervals,  but  their 
action  must  be  intermittent,  and  they  are 
usually  neglected. 

It  is  questionable  whether  the  small 
additional  cost  of  providing  a  steam  plant 
with  an  efficient  drainage  system  as  above 
described  could  be  invested  to  better  ad- 
vantage. It  will  insure  a  positive  saving  by 
reducing  the  initial  condensation  in  the  en- 
gine; it  will  insure  better  cylinder  lubrica- 
tion with  a  reduced  supply  of  oil;  and  it 
will  return  the  water  of  condensation  to  the 
boilers  at  practically  steam  temperature.  It 
will  eliminate  the  straining  of  pipes  due 
to  cooling  when  engines  are  shut  down,  hence 


216 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


obviate  leaks;  and  it  will  remove  all  danger 
of  wrecking  engines  by  water. 

Size  of  Steam  Pipes — The  larger  the  pipe, 
the  greater  the  surface,  hence  the  greater 
the  amount  of  condensation.  The  usual 
practise  is  to  limit  the  steam  velocity  in 
mains  to  6,000  feet  per  minute,  yet  there  are 
many  cases  where  this  figure  could  be  in- 
creased with  advantage.  That  this  is  not 
more  frequently  done  is  due  to  the  impression 
that  drop  of  steam  pressure  causes  a  loss  of 
energy.  In  the  explanation  of  the  throttling 
calorimeter,  page  79,  it  was  shown  that 
there  is  no  loss,  because  the  difference  in 
energy  between  the  steam  at  the  higher 
and  lower  pressures  is  converted  into  heat 
which  evaporates  moisture  and  superheats 
the  steam.  But  if  the  pressure  drop  is  in- 
creased the  steam  velocity  is  also  increased, 
hence  the  pipe  area  is  decreased;  but  in  that 
case  the  exposed  surface  is  also  decreased, 
hence  the  amount  of  condensation  is  pro- 
portionately decreased.  Therefore,  by  in- 
creasing the  drop  in  pressure,  the  condensa- 
tion is  not  only  decreased,  but  the  heat 
liberated  by  the  drop  will  evaporate  all  or 
part  of  the  water  which  is  formed,  hence  the 
steam  which  reaches  the  engine  will  be  drier 
than  if  it  had  been  delivered  through  a  larger 
pipe;  consequently  the  drop  in  pressure 
causes  an  actual  saving  in  heat  instead  of 
a  loss.  To  deliver  the  steam  at  the  engine 
at  a  given  pressure  it  is  necessary  only  to 
increase  the  boiler  pressure  by  the  amount 
of  the  drop,  and  if  this  be  done  it  is  evident 
that  the  size  of  steam  mains  and  the  resulting 
condensation  will  both  be  decreased,  with 
consequent  improvement  in  tne  action  of 
the  engine.  When  steam  is  to  be  conveyed 
through  long  lines  of  piping  the  advantage 
of  raising  the  boiler  pressure  and  keeping 
the  mains  small  will  be  very  marked.  The 
entire  method  is  exactly  parallel  to  standard 
practise  in  electrical  distributing  systems, 
where  the  generator  voltage  is  adjusted 
to  suit  the  loss  in  the  feeder  lines;  this  loss 
corresponds  to  the  drop  in  pressure  in  the 
steam  pipe,  and  by  reason  of  the  drop  both 
feeder  wire  and  the  steam  pipe  can  be  of 
reduced  size.  At  the  electrical  receiving 
station  a  storage  battery  is  often  installed, 
and  its  analogue  in  the  steam  plant  is  a 
receiving  drum  placed  near  the  engine.  The 


effect  of  this  drum  is  to  cause  a  nearly  con- 
stant flow  of  steam  through  the  pipe  which 
connects  it  to  the  boiler  or  main  header, 
while  the  engine  draws  out  steam  inter- 
mittently. The  action  is  more  fully  de- 
scribed under  caption  "Boilers  Supplying 
Hoisting  Engines,"  page  209,  and  is  worthy 
of  careful  study.  To  carry  the  analogy  still 
farther,  it  is  known  that  in  an  electrical 
distribution  system  covering  a  wide  area, 
storage  batteries  installed  at  particular  points 
absorb  energy  when  there  is  a  surplus,  and 
liberate  it  when  there  is  a  deficiency,  and 
thus  steady  the  voltage  on  the  entire  system, 
and  obviate  necessity  of  supply  mains  of 
excessive  size.  In  precisely  the  same  way 
a  steam  pipe  system  can  be  designed  so  that 
storage  drums  at  ends  of  long  lines,  etc., 
will  receive  steam  during  the  time  the  engine 
cut-off  is  in  action,  and  thereby  steady  the 
pressure,  and  enable  the  pipe  sizes  to  be  so 
reduced  that  the  area  of  exposed  surface 
saved  in  the  pipe  exceeds  that  added  by  the 
drum,  hence  not  only  will  the  pressure  at 
the  engine  be  kept  more  steady  and  the 
vibrations  of  the  pipe  be  reduced,  but  the  con- 
densation will  be  decreased,  and  the  removal 
of  the  water  which  is  formed  will  be  more 
easily  accomplished.  There  are  many  cases 
in  all  kinds  of  plants  where  a  practical  ap- 
plication of  these  principles  would  greatly 
improve  the  operation  of  the  machinery. 

The  Constructive  Details  of  steam  piping 
have  been  so  well  worked  out  that  only  the 
leading  points  need  be  touched  upon.  The 
defects  usually  noted  are  flanges  which  are 
too  light,  and  inadequate  provision  for  ex- 
pansion. The  use  of  pipe  bends  of  long 
radii,  instead  of  cast  elbows,  is  becoming 
more  general,  and  they  can  usually  be  so 
placed  as  to  take  up  all  the  expansion  without 
the  use  of  slip-joints  with  stuffing  boxes. 
The  latter  almost  invariably  cause  trouble; 
if  their  use  is  compulsory  the  pipe  must  be 
so  anchored  that  the  slip-joint  cannot  pull 
itself  apart. 

Duplicate  Pipe  Systems  are  now  seldom 
installed.  They  increase  first  cost,  multiply 
the  number  of  valves  and  joints,  increase 
the  condensation,  and  are  of  questionable 
utility.  It  will  generally  be  found  that  the 
same  or  less  money,  if  invested  in  a  single 
pipe  system  properly  designed  and  built,  will 


AUTOMATIC    BOILER   STOP    VALVES 


insure  equally  good  service  at  a  lower  cost 
for  maintenance. 

Valves  should  be  so  located  that  they  can- 
not form  water  pockets  when  either  opened  or 
closed.  Globe  valves  cause  a  drop  of  pres- 
sure, but  as  explained,  this  does  not  cause  a 
loss  of  energy,  but  a  conversion  of  it  into  heat ; 
the  globe  forms  a  water  pocket  unless  it  is  set 
with  its  stem  horizontal,  while  a  gate  valve 
may  be  set  with  spindle  vertical  or  at  an 
angle  as  occasion  demands.  Valves  over  5 
to  6  inches  diameter  should  be  provided  with 
by-pass,  to  enable  them  to  be  easily  opened, 
and  to  permit  steam  to  be  admitted  very 
slowly  into  the  pipe  which  can  thereby  be 
gradually  warmed  up,  and  prevent  water 
hammer. 

Boiler  Valves  —  The  feed  valve  should 
always  be  a  globe.  A  gate  valve  cannot  be 
closely  regulated,  and  often  clatters  owing 
to  the  pulsations  of  the  feed  pump. 

Boiler  stop  valves  should  be  so  placed  that 
water  cannot  collect  above  them.  Thus, 
if  the  pipe  rises  for  a  distance  above  the 
boiler  nozzle  before  turning  horizontal,  the 
stop  valve  should  be  in  the  horizontal  run. 
When  a  long  bend  leads  out  of  the  boiler 
nozzle  the  stop  valve  should  be  at  the  highest 
point  of  the  bend.  When  it  is  impossible 
to  avoid  locating  the  valve  so  that  water  can 
accumulate  above  it  when  closed,  a  drain 
pipe  should  be  provided.  The  best  practise 
is  to  provide  two  valves,  one  placed  as  near 
the  boiler  as  practicable,  and  the  other  at 
the  junction  of  the  boiler  pipe  and  the  main 
header,  with  a  drain  pipe  placed  between  the 
two  valves  to  remove  any  water  due  to 
leakage  through  the  header  valve. 

Automatic  Stop  Valves  are  coming  more 
into  use,  and  in  some  European  countries 
their  installation,  when  several  boilers  are 
operated  together,  is  prescribed  by  law. 
When  several  boilers  feed  into  the  same 
header  it  is  evident  that  if  a  tube  ruptures 
the  steam  from  the  main  will  rush  toward  the 
disabled  boiler,  hence  all  the  boilers  will  tend 
to  discharge  through  the  one  which  is  dis- 
abled. The  sudden  rush  of  steam  thus  caused 
will  lift  water,  which  may  be  swept  along  to 
the  engine  and  wreck  it.  The  difficulty 
of  closing  the  stop  valve  of  the  disabled 
boiler  is  evident.  This  can  be  obviated  by 
selecting  for  position  nearest  the  boiler  an 


automatic  stop  valve,  which  will  close  when 
the  pressure  in  the  main  slightly  exceeds 
that  in  the  boiler,  and  open  when  the  boiler 
pressure  rises  again.  Such  valves  cost  but 
little  more  than  ordinary  stop  valves,  and 
should  a  tube  fail  in  a  boiler  to  which  such 
a  valve  is  attached  the  operation  of  the  other 
boilers  is  not  affected,  and  nothing  need  be 
done  except  to  allow  the  disabled  boiler  to 
empty  itself. 

TABLE    62 

DIAMETER  AND    DRILLING  TEMPLET 

FOR    EXTRA    HEAVY 

PIPE    FLANGES 

MASTER  STEAMFITTERS'  STANDARD 


Diameter 
of  Pipe 
Inches 

Diameter 
of 
Flanges 
Inches 

Bolt 
Circle 
Inches 

Number 
of  Bolts 

Diameter 
of  Bolts 
Inches 

Length  of 
Bolts 
Inches 

I 

4* 

3i 

4 

4 

2 

li 

5 

3f 

4 

i 

a* 

I* 

6 

4i 

4 

I 

'* 

2 

6* 

5 

4 

1 

»J 

2* 

7* 

si 

4 

a 

4 

3 

3 

8i 

6f 

8 

f 

3 

3i 

9 

7i 

8 

5 

8 

3i 

4 

10 

7i 

8 

1 

3* 

4i 

io£ 

8* 

8 

3 

4 

3^ 

5 

II 

9i 

8 

3 

4 

3f 

6 

iai 

i  of 

12 

a 

4 

4 

7 

14 

"I 

12 

8 

4 

8 

15 

i3 

12 

i 

4i 

9 

16 

14 

12 

8" 

4i 

10 

i7* 

'Si 

16 

1 

4l 

12 

20 

T>73 

J74 

16 

1 

5 

14 

22^ 

20 

20 

1 

Si 

15 

23i 

21 

2O 

I 

Si 

16 

25 

22^ 

20 

I 

si 

18 

27 

24^ 

24 

I 

6 

20 

29^ 

26| 

24 

i* 

61 

22 

34 

28f 

28 

it 

6^ 

24 

34 

3ii 

28 

i* 

6.| 

Note  —  Flanges,  flanged  fittings,  valves,  etc., 
are  drilled  in  multiples  of  four,  so  that  fittings  may 
be  made  to  face  in  any  quarter  and  holes  straddle 
center  line. 


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FIRST   NATIONAL   BANK    BUILDING,  CHICAGO,  ILL.,  OPERATING   1,875    H.  P.  OF  STIRLING    BOILERS 

218 


Boiler  and  Steam  Pipe  Coverings 


When  saturated  steam  is  conveyed  through 
pipes  a  portion  will  condense,  the  amount 
depending  upon  the  temperature  of  the  steam, 
and  the  velocity  and  temperature  of  the  air 
surrounding  the  pipe.  This  condensation 
causes  a  loss  not  only  of  volume  of  steam, 
but  of  efficiency  in  utilizing  the  remainder 
of  the  steam  when  it  reaches  the  engine,  con- 
sequently where  fuel  economy  is  an  object 
all  steam  pipes,  boiler  steam  drums,  re- 
ceivers, etc,,  should  be  covered  with  some 


For  practical  purposes  3  B.  T.  U.  per  hour 
may  be  assumed.  To  determine  the  money 
value  of  the  loss  in  any  particular  case,  de- 
termine the  square  feet  of  exposed  pipe  surface ; 
determine  the  temperature  of  the  steam,  by 
referring  to  Steam  Table,  page  74,  assume 
the  average  temperature  of  the  air  sur- 
rounding the  pipe,  and  then  compute  the 
temperature  difference.  Conditions  of  oper- 
ation of  the  plant  will  approximately  de- 
termine the  number  of  hours  per  annum 


TABLE  63 
EXPERIMENTS    ON    STEAM    PIPE    COVERING* 


B.  T.  U.  per  Hour 

Kind  of  Covering. 

Diam.  of 
Test  Pipe. 
Inches. 

Thickness 
of  Covering 
Inches. 

Temperatures  Fah. 

per  Square  Foot  of 
Pipe  Surface. 

Date  of 
Test. 

Testing 
Expert. 

Steam  . 

Air. 

Total. 

Per  Degree 
Difference. 

Hair  Felt          .... 

2 

o  .96 

302.8 

71  -4 

89.6 

0.387 

1901 

Jacobus 

"       "              .... 

8 

0.82 

348-3 

69  .  o 

117.9 

o  .422 

1894 

Brill 

Remanit  for  intermediate  p  essure 

2 

0.88 

304  .  5 

73-3 

100.3 

0-434 

190 

Jacobus 

'     high  pressure 

2 

.30 

306.6 

76.! 

83.7 

0.363 

190 

Jacobus 

Mineral  Wool         ... 

& 

•  30 

344- 

58.3 

81.3 

o.  284 

1894 

Brill 

Champion  Mineral  Wool 

s 

.44 

34<3. 

74-3 

86.  i 

0.317 

1894 

Brill 

Rock  Wool 

8 

.60 

344  • 

63  .  o 

72.O 

O.256 

1  89^ 

Brill 

Asbestos  Sponge  Felted 

2 

•  I25 

364- 

60  .  7 

145-Q 

0.477 

190 

Barrus 

"              "             "      . 

IO 

•  375 

364. 

62.8 

85.0 

o  .  248 

190 

Barrus 

"                            "      .            . 

2 

•  14 

309. 

79-4 

SQ-7 

o  .  260 

190 

Jacobus 

Magnesia.         .... 

4 

.  I  2 

388. 

72  .0 

147.0 

0.465 

1896 

Norton 

" 

2 

•  °9 

354  • 

80.  I 

155-8 

o  •  5^7 

1896 

Paulding 

" 

8 

25 

S44  . 

66.3 

1  06  .  6 

o    "?8i 

i  So 

Brill 

" 

2 

.08 

310  . 

81  .6 

69^8 

^  .  j«.»*f 
0.304 

i  uy 
I9O 

Jacobus 

. 

2 

.00 

365. 

64.6 

155-0 

0.515 

1  90 

Barrus 

Asbestos,  Navy  Bran  !     . 

IO 
2 

.19 

.  20 

365- 
309. 

66.0 
79-4 

103.0 
69.9 

0-347 
0.304 

190 
190 

.  Barrus 
Jacobus 

. 

2 

•  125 

365- 

64.6 

176.0 

0.585 

190 

Barrus 

*  '             "           "      •,  . 

IO 

•  375 

365. 

66.8 

I  12  .0 

o.  375 

190 

Barrus 

Manville  Sectional 

8 

.70 

345- 

78.3 

93  -4 

0.394 

1894 

Brill 

. 

2 

•  3i 

354. 

80.  I 

157-0 

0.572 

1896 

Paulding 

Asbestos  Air  Cell 

4 

4 

•  25 

.  12 

388. 
388. 

72.0 
72.0 

143.0 
1  66.0 

0-453 
0.525 

1896 
1896 

Norton 
Norton 

Asbestos  Fire  Felt 

2 

8 

.96 
•  30 

303.3 
344.7 

72.3 
79.0 

165.5 
133-5 

0.716 
0.502 

1901 
1894 

Jacobus 
Brill 

2 

.  oo 

354-7 

80.  i 

198.0 

o.  721 

1896 

Paulding 

Fossil  Meal           ... 
Riley  Cement         ... 

2 

8 

8 

.90 

•75 
•75 

307.4 
347  •  I 
347-9 

72-5 
75-3 
74.3 

180.0 
238.0 
260.0 

0.766 
0.876 
0.950 

1901 

1894 
1894 

Jacobus 
Brill 
Brill 

efficient  heat  insulating  material,  and  the 
saving  thus  effected  will  pay  large  interest 
on  the  investment. 

It  has  been  experimentally  determined  that 
each  square  foot  of  bare  iron  pipe  surface 
will  radiate  about  3  British  thermal  units 
per  hour  for  each  degree  Fahr.  difference 
between  the  temperatures  of  the  steam  and 
the  outside  air,  the  exact  amount  varying 
with  the  velocity  and  humidity  of  the  air. 


during  which  steam  will  be  in  the  pipe  line, 
hence  the  total  B.  T.  U's  lost  per  annum 
can  be  roughly  determined.  This  divided 
by  965.8  will  give  the  number  of  pounds 
of  steam  from  and  at  212°  equivalent  to  this 
loss;  the  evaporation  per  pound  of  coal  and 
the  cost  of  coal  per  ton  (including  cost  of 
handling  it  and  ashes)  being  known,  the 
money  value  of  the  loss  is  at  once  derived. 
Or  expressing  the  matter  in  a  formula: 


*Arranged  from  data  given  in  Paulding's  Condensation  of  Steam  in  Covered  and  Bare  Pipes. 


KINDS    OF    PIPE    COVERING 


221 


Cost     per     annum  of     steam    condensed= 
-  f     } 


In  which  .4=area  of  exposed  pipe  surface  in 

square  feet. 

^temperature  Fah.  of  steam. 
^=average  temperature  Fah.  of  sur- 

rounding air. 

A/=hours    per    annum   steam  is  in 
the  pipe  line. 

£=evaporation    from    and  at   212° 
Fah.  per  Ib.  of  coal. 

C=cost     of     coal      and     handling, 
per  ton. 

For  long  tons  the  constant  2,000  should 
be  changed  to  2,240. 

By  properly  applying  a  covering  of  good 
grade,  as  much  as  90  per  cent,  of  this  may  be 
saved.  There  are  many  brands  of  covering 
on  the  market,  and  the  only  practical  way 
to  be  sure  of  what  each  will  do  is  either  to 
purchase  of  a  firm  of  established  integrity, 
or  else  make  comparative  tests.  If  the  co- 
efficient of  conductivity  of  a  covering  is 
known,  the  heat  loss  for  any  given  set  of 
conditions  can  be  calculated,  but  the  com- 
putation is  tedious  and  the  results  are  only 
approximate.  The  method  of  using  this 
coefficient,  and  of  determining  it  by  experi- 
ment, may  be  found  in  Paulding's  Con- 
densation of  Steam  in  Covered  and  Bare  Pipes, 
together  with  curves  showing  the  relation 
between  thickness  of  covering  and  the  heat 
loss,  and  other  interesting  information  on 
the  transmission  of  heat. 

It  is  questionable,  however,  whether  in- 
tricate calculations  of  the  heat  loss  from 
pipes  are  of  great  practical  utility,  owing  to 
the  impossibility  of  assigning  sufficiently 
close  values  to  the  factors  which  affect  all 
such  calculations.  About  all  that  can  be 
done  is  to  determine  with  a  fair  degree  of  ap- 
proximation the  relative  amount  of  heat 
lost  by  bare  and  covered  pipes.  Table  63 
has  been  compiled  from  tests  made  by  various 


authorities,  and  for  each  covering  the  B.  T. 
U.'s  transmitted  per  square  foot  of  pipe  sur- 
face per  hour  per  degree  difference  between 
the  steam  and  air  temperatures  have  been 
computed  and  entered  in  the  table.  Since 
bare  pipe  loses  3  B.  T.  U.  per  hour  per  square 
foot  per  degree  difference  in  temperature, 
the  per  cent,  of  heat  saved  by  the  covering 
can  be  computed  with  sufficient  accuracy  for 
all  practical  purposes.  In  case  of  an ,  un- 
known covering  the  heat  loss  per  degree  of 
difference  can  be  determined  experimentally. 

There  is  a  dearth  of  accurate  data  on  the 
life  of  pipe  coverings  of  different  kinds.  It 
is  well  known,  however,  that  as  a  result  of 
constant  vibrations,  some  of  them  when  on 
horizontal  pipes  lose  their  shape,  hang  loose 
on  the  pipe,  and  allow  the  material  to  shift 
so  that  the  covering  becomes  thicker  on  the 
bottom  than  on  the  top.  Only  previous 
experience  or  careful  inquiry  as  to  the  ex- 
perience of  others  can  indicate  what  defects 
of  this  nature  may  develop  in  a  covering 
after  it  has  long  been  at  work. 

Pipe  coverings  may  be  either  "sectional" 
that  is,  moulded  to  shape,  and  attached  to 
pipes  by  bands,  etc.,  so  it  can  be  removed  at 
any  time,  or  "plastic"  which  is  mixed  in 
shape  of  mortar,  and  built  up  on  the  pipe  in 
layers,  so  that  it  cannot  be  removed  and 
replaced  without  working  it  over.  The 
former  has  more  joints,  and  often  under 
vibration  changes  shape,  but  is  more  con- 
venient for  work  subject  to  future  altera- 
tion. The  plastic  covering  obviates  joints, 
adheres  closely  to  the  pipe  if  of  proper  quality 
and  workmanship,  needs  few  repairs,  and 
the  thickness  can  be  varied  to  suit.  It  is 
more  difficult  to  apply  than  sectional  cover- 
ing but  more  permanent  when  applied. 

Pipe  coverings  should  receive  the  same 
care  and  frequent  inspection  as  any  other 
part  of  a  plant.  Their  efficiency  quickly 
falls  off  if  air  is  allowed  to  circulate  between 
them  and  the  pipe,  and  if  allowed  to  become 
wet  they  only  increase  the  evil  they  are 
expected  to  remedy. 


Boiler  Cleaning 


No  boiler  can  maintain  its  efficiency  un- 
less it  is  kept  clean  both  inside  and  out. 
Deposits  of  solid  matter  on  the  water  side  of 
the  heating  surface  interfere  with  the  heat 
transmission,  and  cause  the  metal  to  burn, 
blister,  or  crack,  thereby  greatly  increasing 
the  repair  and  fuel  bills.  Systematic  boiler 
cleaning  should  therefore  be  included  as  a 
regular  feature  of  the  operation  of  every 
steam  plant,  and  for  the  purpose  of  assist- 
ing those  who  do  this  work  the  following 
suggestions  are  offered. 

Cutting  Boilers  out  of  Service  Prepara= 
tory  to  Cleaning — A  boiler  should  never 
be  emptied  while  the  brickwork  is  hot;  if 
this  be  done  there  will  be  danger  of  over- 
heating the  metal,  and  the  incrustation  will 
bake  to  such  hardness  as  greatly  to  increase 
the  difficulty  and  expense  of  removing  it. 

The  best  procedure  is  to  allow  the  boiler 
to  stand  at  least  twelve  hours,  and  more  if 
possible,  after  the  fires  are  drawn,  then  to 
empty  it  slowly;  the  manhole  plates  should 
then  be  removed,  and  the  interior  be  thor- 
oughly washed  out  with  cold  water,  after 
which  the  use  of  the  turbine  cleaner  should  be 
started.  If  this  plan  requires  a  longer  time 
than  is  available,  the  next  best  method  is  to 
allow  the  boiler  to  stand  three  or  four  hours 
after  the  fires  are  drawn  and  the  main  stop 
valve  is  closed;  the  pressure  should  then  be 
let  off,  the  blow-off  valves  be  opened  slightly 
and  water  be  pumped  in  at  the  same  rate 
as  it  is  escaping  from  the  blow-off,  which 
can  be  done  by  regulating  the  pump  to  the 
speed  necessary  to  hold  the  water  at  the 
same  level  in  the  gauge  glass.  Pumping 
should  be  continued  until  the  boiler  is  cooled 
to  a  temperature  low  enough  to  permit  it  to 
be  opened  and  washed  with  cold  water,  and 
the  use  of  the  cleaner  should  then  begin. 

To  hasten  the  cooling  of  the  boiler  it  is 
not  unusual  to  open  the  fire  and  ash-pit  doors 
and  the  damper,  thus  causing  a  rush  of  cold 
air  through  the  setting.  While  this  assists 
in  the  cooling,  it  is  an  unsuspected  cause  of 
the  destruction  of  many  furnace  walls.  A 
rush  of  cold  air  over  highly  heated  fire-brick 
causes  a  rapid  cooling  of  the  exposed  sur- 


faces, uneven  shrinkage,  and  cracking  or 
"spalling"  of  the  brick  and  loosening  of  the 
joints.  The  degree  to  which  these  evil 
effects  are  caused  by  cold  air  is  not  generally 
recognized,  and  it  is  advisable  never  to  throw 
open  the  damper  and  draft-doors  until  about 
four  hours  after  the  fires  are  drawn. 

Before  starting  to  remove  a  manhole  plate 
the  operator  should,  by  trying  the  gauge 
cocks,  or  by  opening  the  valve  on  the  steam 
hose  connection,  definitely  ascertain  that 
there  is  neither  a  steam  pressure  nor  a 
vacuum  inside  of  the  boiler.  A  disregard  of 
this  simple  precaution  has  been  responsible 
for  many  serious  accidents  to  those  engaged 
in  cleaning  boilers. 

Cleaning  the  Interior — Practically  all 
waters  available  for  boiler  feeding  contain 
some  impurities  which  deposit  either  as 
mud  or  as  scale.  When  mud  is  present  it 
is  nearly  always  precipitated  into  the  lower 
drum  of  the  Stirling  boiler,  whence  it  should 
be  blown  out.  at  regular  intervals  which  must 
be  determined  by  close  observation  in  each 
case.  Occasionally  some  mud  adheres  to  the 
rear  bank  of  tubes,  and  this  should  be 
regularly  removed  by  washing  down  with 
water  applied  under  a  good  pressure  through 
a  hose  terminating  in  a  rose-shaped  nozzle. 

Scale  varies  from  a  porous  texture  which 
adheres  loosely  to  the  metal,  to  a  hard  flinty 
structure  which  can  be  removed  only  by 
chiseling  or  cutting  it.  Its  removal  is  often 
tedious  but  the  task  should  never  be  slighted 
Various  ways  of  removing  scale  have  been 
tried,  but  experience  shows  that  the  most 
satisfactory  method  it  to  use  some  mechani- 
cal device,  operated  by  power,  and  so  de- 
signed as  to  cut  or  break  the  scale.  Such 
devices  may  be  divided  into  two  classes: 
(i)  Those  which,  by  very  rapid  hammer 
blows,  detach  the  scale  by  cracking  it;  (2) 
those  which,  after  the  manner  of  an  emery 
wheel  dresser,  cut  the  scale  into  small  pieces. 
Tools  of  the  first-named  kind  have  the  serious 
disadvantage  of  swaging  the  tubes  to  a  larger 
or  irregular  diameter,  producing  crystalliza- 
tion in  the  metal,  and  causing  leaks  where  the 
tubes  are  expanded  into  the  sheets,  hence 


223 


CANDLER    INVESTMENT    CO.'S    BUILDING,   ATLANTA,   GA.,   OPERATING    6OO    H.    P.   OF    STIRLING    BOILERS 

224 


OPERATING    THE    TURBINE    CLEANER 


225 


their  use  is  not  to  be  recommended.  Tools 
of  the  second-named  class  are  preferable, 
and  of  these  the  most  satisfactory  is  the 
hydraulic  turbine  tube-cleaner. 

Hydraulic  Turbine  Tube=Cleaner — This 
is  made  in  many  designs,  one  of  which  is 
shown  in  Fig.  45.  The  cylindrical  casing 
contains  a  hydraulic  turbine,  consisting  of  a 
fixed  guide  plate  which  directs  the  water  at 
the  proper  angle  upon  the  vanes  of  the 
rotating  wheel.  The  water  is  supplied 
through  a  wire-wound  rubber  hose  attached 
to  the  upper  end  of  the  casing,  and  the  power 
generated  in  the  turbine  is  transmitted, 
through  a  universal  joint,  to  a  cross-shaped 
head  which  carries  four  pivoted  arms  to  the 
extreme  end  of  which  the  cutters  are  at- 
tached. This  construction  makes  the  tool 
perfectly  flexible,  so  that  with  equal  facility 
it  will  pass  through  either  a  straight  or  curved 


into   a   sump    or   sunken  tank,  in    which    it 
can  settle  and  be  used  repeatedly. 

Piping      for      Supplying     the     Water — 

In  many  cases  the  turbine  is  operated  by 
two  men,  one  in  the  boiler,  and  another 
outside  to  turn  the  water  on  and  off  as . 
required.  This  method  not  only  requires 
one  man  more  than  is  necessary,  but  causes 
waste  of  time  in  giving  orders  to  operate 
the  water  valve.  A  much  better  plan  is 
to  locate  along  the  rear  of  the  boilers  a 
pipe  conveying  the  water,  and  to  provide 
this  pipe  with  branches  opposite  the  middle 
of  each  aisle  between  boilers.  On  these 
branches  place  a  plug  valve,  upon  the 
stem  of  which  an  S-shaped  handle  about 
1 8  inches  long  can  be  placed  whenever 
cleaning  is  to  be  done.  A  piece  of  light 
rope  tied  to  each  end  of  this  handle  is  ex- 
tended into  the  boiler  drums,  and  by  pulling 


FIG.  45.     HYDRAULIC  TURBINE  TUBE   CLEANER 


tube.  The  thrust  on  the  working  parts  is 
taken  upon  ball  bearings  or  on  hardened 
steel  rings,  placed  between  the  turbine  wheel 
and  the  guide  plate. 

The  cutters  used  under  normal  conditions 
are  hardened  steel  toothed  disks,  similar 
to  those  used  for  emery  wheel  dressers,  as 
shown  in  Fig.  46.  In  special  cases  other 
forms  of  cutters  are  used,  as  later  described. 

When  the  turbine  is  revolving  at  a  high 
speed,  the  pivoted  arms  are  thrown  out,  and 
the  cutters,  through  centrifugal  force,  bear 
upon  the  surfaces  to  be  cleaned  and  chip 
away  the  scale  in  small  pieces.  The  stream 
of  water  flowing  from  the  turbine  envelops 
the  cutters,  keeps  their  edges  cool,  and 
washes  away  the  scale  as  fast  as  it  is  de- 
tached. 

In  arid  countries,  where  water  is  scarce, 
the  overflow  from  the  turbine  may  be  run 


these  ropes  the  operator  regulates  the  water 
to  suit  himself,  wastes  no  time  in  giving 
orders,  and  but  one  man  is  required.  The 
pipe  supplying  the  water  should  be  free  from 
reducers,  and  the  hose  connection  should 
be  full  size 

Operating  the  Cleaner — Always  use 
the  largest  size  of  turbine  which  will  pass 
through  the  tubes.  When  cleaning  begins 
the  turbine  should  be  inserted  into  the 
end  of  a  tube,  and  the  operator  should 
have  a  firm  grasp  on  the  hose  within  6  or 
8  inches  of  the  tube  end.  When  the  water 
is  turned  on,  the  rotating  parts  begin  to 
revolve,  the  cutter  arms  fly  out,  and  the 
attack  on  the  scale  begins.  The  operator 
should  then  immediately  begin  moving  the 
turbine  alternately  up  and  down  and  con- 
tinue this  as  long  as  the  tool  is  working. 
The  water  should  not  be  cut  off  while  the 


>vT^  H 

f  OF  THE 

f  UNIVERSITY 


HOW  TO  SOFTEN  REFRACTORY  SCALE 


227 


cleaner  is  in  the  tube,  nor  should  the  cleaner 
be  permitted  to  remain  stationary  -  -  it 
must  be  kept  constantly  moving  up  and 
down.  As  the  scale  is  removed,  the  turbine 
will  gradually  travel  farther  down  the  tube, 
and  when  it  finally  reaches  the  mud  drum 
the  tube  will  be  clean,  unless  the  tool  has 
been  either  pushed  through  too  fast,  or 
allowed  to  draw  itself  through.  Usually 
the  weight  of  the  tool  and  hose  will  tend 
to  draw  the  turbine  down,  and  if  allowed 
to  go  ahead  too  fast,  it  may  remove  the 
scale  from  a  spiral-shaped  strip,  leaving 
it  in  other  places,  hence  it  is  important 
that  the  operator  train  himself  to  detect 
by  the  sound,  and  vibration  of  the  hose, 
the  character  of  the  surface  upon  which 
the  cleaner  is  working,  and  to  regulate  the 
forward  motion  of  the  cleaner  accordingly. 

The  toothed  disk  cutters  give  entirely  sat- 
isfactory results  when  the  scale  does  not 
exceed  ^-inch  in  thickness,  which  covers 
all  cases  of  normal  use,  since  except  in  an 
emergency,  scale  exceeding  |  to  T3g-inch 
thick  should  never  be  allowed  to  form  in  the 
rear  bank  of  tubes  between  regular  clean- 
ings, and  TV-inch  thickness  of  scale  on  tubes 
in  the  front  or  middle  bank  is  prima  facie 
evidence  that  the  boiler  has  been  neglected. 
In  cases  of  neglect,  not  only  will  a  greater 
thickness  of  scale  form,  but  by  long  ex- 
posure to  heat  it  bakes  harder  than  other- 
wise, which  greatly  increases  the  difficulty 
and  expense  of  removing  it.  As  soon  as 
a  boiler  is  found  to  be  heavily  scaled,  it 
should  at  once  be  cut  out  of  service  and 
cleaned.  If  it  is  found  that  the  scale  does 
not  exceed  f-inch  thick,  the  toothed  disk 
cutters  should  be  replaced  by  solid  conoidal 
cutters,  made  of  tool  steel,  as  in  Fig.  47. 
Place  these  with  the  small  end  downward. 

Should  the  scale  exceed  f-inch  in  thickness, 
it  is  best  removed  by  a  four-lipped  drill, 
made  of  hardened  tool  steel,  with  cutting 
edges  at  an  angle  of  45  degrees  to  the  axis 
of  the  tool,  as  in  Fig.  48.  When  the  scale 
is  excessively  thick,  it  should  first  be  attacked 
by  using  a  drill  head  of  the  form  shown  in 
Fig  49.  which  should  be  followed  by  Fig.  48. 

The  tools  represented  in  Figs.  48  and  49 
are  fastened  to  the  turbine  by  removing 
the  cross-shaped  piece  which  carries  the  arms, 
and  substituting  the  head  to  which  the 


drill  is  attached.  When  using  these  tools 
on  heavy  scale  the  turbine  should  be  handled 
with  judgment,  as  it  is  evident  that  the 
tool  cannot  be  advanced  as  rapidly  as  when 
the  scale  is  thin . 

By  careful  observance  of  the  foregoing 
instructions  it  will  be  possible  to  remove 
any  deposit  found  in  a  tube,  but  the  time 
required  will  of  course  vary  according  to 
the  nature  of  the  scale,  and  the  thickness 
to  which  it  has  been  allowed  to  accumulate. 

Care  of  the  Turbine  Cleaner — Those 
who  have  had  no  experience  with  turbine 
cleaners  are  advised  to  take  the  tool  apart, 
and  familiarize  themselves  with  its  con- 
struction. While  the  tool  is  well  built, 
it  must  be  properly  cared  for  if  satisfactory 
results  are  to  be  obtained.  When  each 
boiler  cleaning  is  finished,  the  turbine  should 
be  thoroughly  washed,  then  stored  in  a 
pail  of  oil. 

How  to  Soften  Refractory  Scale — When 
scale  has  been  allowed  to  accumulate  and 
bake  to  an  excessive  hardness  its  removal 
is  difficult,  The  work  may  be  expedited 
by  introduction  of  some  agent  which  will 
rot  and  soften  the  scale.  One  method 
is  to  introduce  40  to  80  Ibs.  of  carbonate 
of  soda  (ordinary  soda-ash)  according  to 
size  of  the  boiler,  block  the  safety  valves 
open,  then  allow  the  water  to  simmer  gently; 
in  a  particularly  bad  case  this  may  require 
several  day's  boiling.  The  scale  will  thus 
be  softened  so  that  it  can  easily  be  cut;  the 
boiler  should  finally  be  thoroughly  rinsed 
with  fresh  water,  or  foaming  may  result. 

Kerosene  is  often  used  for  the  same 
purpose.  Some  spray  it  over  the  surface 
with  a  squirt  pump,  or  other  means,  while 
some  fill  the  boiler  nearly  full  of  water, 
introduce  a  quantity  of  kerosene,  then 
open  the  blow-off  valve  very  slightly,  so 
that  as  the  water  level  slowly  falls  the 
kerosene  is  brought  into  contact  with  every 
portion  of  the  interior  surface.  Before  one 
enters  the  boiler  it  should  be  thoroughly 
ventilated  to  remove  volatile  gases  from 
the  oil,  since  they  are  highly  explosive. 

Kerosene  should  never  be  used  without 
first  testing  it  for  free  acid  which  is  liable  to 
be  present  from  the  refining.  Insert  blue 
litmus  paper,  and  if  it  turns  red  the  oil  should 
be  rejected  since  the  acid  will  cause  corrosion. 


15 


228 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


Oil  in  Boilers — Scale  is  not  the  only 
cause  of  burned  tubes.  Burnt  and  blistered 
tubes  will  be  the  inevitable  result  of  allowing 

011  to    enter    boilers.     When    the    presence 
of  oil  is  detected  the  boiler    should  at  once 
be  cut  out  of  service,  and  as  soon  as  it  has 
cooled    it    should    be    emptied,    and    several 
pailfuls    of    soda-ash    be    placed    into    the 
mud    drum.     The    boiler    should    then    be 
filled   with    water,    and    be    gently    fired    for 

12  to   15  hours,  keeping  the  steam  pressure 
down    to    12    or    15    pounds.     At    intervals, 
a  portion  of  the  water  may  be  let  out,  and 
be   replaced   by   pumping   in    an   equivalent 
amount;  finally  the  boiler  should  be  allowed 
to   cool,   then   be   emptied   and   the   interior 
be  thoroughly  rinsed  with  fresh  water. 

Cleaning  the  Fire  Side  of  the  Heating 
Surface — The  fire  side  of  the  heating  sur- 
face should  be  kept  clean,  and  under  no 
circumstances  should  a  thickness  of  soot 
exceeding  ^V  of  an  inch  be  allowed  to  form, 
or  the  boiler  efficiency  will  be  greatly  de- 
creased. The  surface  of  the  tubes  and 
drums  should  be  regularly  blown  off  with 
steam  by  using  the  hose  and  steam  blower- 
pipe  furnished  with  the  boiler.  Since  the 
heating  surface  can  be  blown  off  in  10  to 
15  minutes,  there  is  no  reason  for  neglecting 
this  work.  The  interval  between  such  clean- 
ings will  depend  upon  the  character  of  the 
fuel;  with  smoky  fuels  the  cleaning  should 
be  done  at  least  once  per  day,  preferably 
during  the  period  of  lightest  load;  the  sur- 
face should  also  be  well  brushed  off  at  reg- 
ular intervals. 

Never  use  the  steam-blower  when  the  boiler 
is  cold,  or  the  steam  will  condense,  dam- 
pen the  brickwork,  and  cause  the  sooty 
deposits  to  become  gummy  and  adhere 
to  the  metal.  It  is  advisable  to  have  not 
less  than  50  pounds  pressure  on  the  boiler 
when  the  steam-blower  is  used,  and  there 
should  be  a  fire  on  the  grates  to  insure  the 
brickwork  being  hot. 

Necessity  for  Periodical  Examinations 
— No  matter  how  excellent  the  feedwater 


may  appear  to  be,  every  boiler  should  at 
regular  intervals  be  examined,  and  even 
though  no  trace  of  deposit  be  noted  the 
cleaner  should  be  passed  through  the  tubes, 
to  ascertain  their  condition,  and  enable 
one  to  know  that  they  are  clean. 

The  mud  drum  should  be  inspected  reg- 
ularly, and  all  accumulation  of  soot,  ashes, 
or  dirt,  be  thoroughly  removed.  In  all 
cases  where  coal,  particularly  anthracite, 
is  used,  the  accumulations  on  the  mud 
drum  should  be  blown  off  before  the  boiler 
is  emptied.  The  reason  for  this  is  that 
such  deposits  often  contain  coal  which 
holds  fire  for  many  hours  after  the  furnace 
fires  are  drawn,  and  the  heat  due  to  this 
cause  may  damage  the  drum  or  tube  ends 
if  the  boiler  is  emptied. 

All  soot,  ashes  and  dirt  should  be  removed 
from  the  top  of  furnace  arches  every  time 
the  boiler  is  cleaned.  The  top  of  the  bridge 
wall  should  be  swept  clean,  and  any  defects 
in  the  brickwork  should  be  repaired.  The 
asbestos  rope  joint  between  brickwork  and 
ends  of  the  mud  drum  should  be  inspected, 
and  unless  found  perfectly  air  tight,  it 
should  be  made  so  before  the  boiler  goes 
into  service.  The  opening  where  the  blow- 
off  pipe  passes  through  the  wall  should  be 
inspected,  and  if  air  leaks  are  found  they 
should  be  stopped  by  caulking  with  asbestos 
rope.  All  cleaning  doors  should  be  examined, 
and  if  air  leaks  are  detected  they  should 
be  stopped. 

Whenever  a  boiler  is  off  for  cleaning  it 
is  an  excellent  plan  to  make  a  careful  general 
inspection  of  it  both  inside  and  out,  in- 
cluding the  setting,  cleaning  doors,  valves 
fittings,  etc.  Incipient  defects  may  thus 
be  discovered  and  corrected  at  a  trifling 
expense,  serious  troubles  will  be  obviated, 
and  the  general  operation  of  the  plant  will 
be  improved.  It  is  doubtful  whether  the 
short  time  necessary  for  such  inspection  could 
be  more  profitably  employed,  since  a  boiler 
plant  continually  proves  the  truth  of  the 
ancient  maxim,"  A  stitch  in  time  saves  nine.' ' 


Care  and  Management  of  the  Stirling  Boiler 


Before  starting  a  new  Boiler — Make  a 
complete  examination  of  boiler  and  setting. 
Inspect  all  valves,  fittings  and  attachments, 
and  ascertain  that  they  are  properly  connected 
and  in  perfect  order.  See  that  nuts  on  all 
tie  rods  in  frame  are  turned  up  tight,  and 
at  intervals  during  the  first  six  months  after 
the  boiler  is  in  operation,  ascertain  if  these 
nuts  are  tight,  and  if  not,  make  them  so. 

Inspect  the  brickwork,  and  see  that 
height  of  fire-arches  and  distance  between 
end  of  fire-arches  and  nearest  tube  corre- 
sponds with  drawings.  Sec  that  the  mud 
drum  can  expand  freely;  that  baffle  openings 
are  as  marked  on  drawings,  baffle  tiles  all 
in  place  and  joints  sealed  with  fire  clay, 
and  that  all  mortar  and  rubbish  which  has 
dropped  down  on  the  mud  drum  while 
brickwork  was  in  progress,  has  been  scraped 
off  and  drum  surface  brushed  clean.  This 
is  frequently  overlooked.  See  that  blow-off 
pipe  and  valve,  as  well  as  blow-off  main  to 
which  they  are  connected,  can  move  freely; 
on  no  account  should  they  be  cemented  or 
bricked  in,  but  should  lie  free  in  a  trench  or 
slot.  See  that  space  around  the  blow-off 
pipe  where  it  passes  through  rear  setting 
wall  is  plugged  with  asbestos  rope  until  it 
is  air-tight. 

When  oil  or  gas  fuel  is  used,  take  par- 
ticular care  to  ascertain:  if  the  fire  arches 
terminate  at  proper  distance  from  the  tubes; 
checkerwork  walls  in  rear  of  grates  are  of 
proper  height;  openings  between  brick  over 
grates  are  of  proper  width,  and  burners  set 
to  blow  the  flame  parallel  to  the  brick  over 
grates  and  at  proper  distance  above  them; 
to  minimize  effect  of  gas  explosions,  turn 
back  the  latches  of  cleaning  doors,  so  the 
doors  can  blow  open  freely  and  release  the 
pressure  due  to  the  explosion. 

See  that  all  dirt,  waste,  and  tools,  are  re- 
moved from  interior  of  boiler.  Then  place 
in  boiler  about  a  peck  of  soda-ash,  fill  to 
usual  level  with  water,  boil  gently  for  several 
hours  after  boiler  is  finally  heated  up,  let 
stand  till  cold,  then  empty,  and  finally  give 
interior  of  boiler  a  thorough  washing  with 
cold  water.  This  will  remove  all  oil  and 


grease  and  prevent  foaming  when  the  boiler 
goes  into  commission. 

Firing  a  Boiler  with  Green  Walls  will 
invariably  crack  the  Setting,  hence  it  is 
absolutely  necessary  to  dry  out  the  brickwork 
properly.  If  circumstances  permit,  it  is 
advisable  as  soon  as  stack  connections  are 
made,  to  block  open  the  damper  and  ash-pit 
doors,  so  that  circulation  of  air  will  aid  in 
drying  the  brickwork.  The  next  step  is  to 
fill  the  boiler  with  water  and  put  in  a  light 
fire  of  shavings,  which  may  gradually  be 
increased  by  using  some  wood,  continuing 
until  the  walls  are  thoroughly  dried  inside 
and  out.  This  will  require  several  days, 
but  by  close  observation  the  walls,  if  built 
according  to  instructions  (page  233)  can  be 
dried  out  without  cracking. 

When  steam  is  available  an  excellent 
method  of  drying  the  brickwork  is  to  connect 
temporarily  a  small  steam  supply  pipe  to 
the  new  boiler,  and  to  attach  a  trap  or  other 
drainage  apparatus  to  the  blow-off  pipe. 
The  new  boiler  when  filled  with  steam  will 
then  act  as  a  large  radiator,  and  will  heat 
the  air  around  it,  hence  if  ash-pit  doors 
and  damper  be  left  open  there  will  be  a 
steady  current  of  warm  air  passing  through 
the  setting,  and  the  brickwork  will  be  grad- 
ually and  effectively  dried  out.  The  steam 
supply  should  be  very  small  at  first,  and 
be  increased  as  the  drying-out  proceeds. 

Cutting  Boiler  into  Steam  Main — Under 
no  circumstances  whatever  should  a  boiler 
be  "cut  in"  with  other  boilers  unless  the 
pressure  within  it  is  identical  with  that  in 
the  main.  Before  opening  the  boiler  stop 
valve  or  the  header  valve,  be  sure  that  there 
is  no  water  in  the  length  of  pipe  between  these 
two  valves.  Steam  valves  should  always 
be  opened  or  closed  very  slowly,  and  the 
valves  should  first  be  eased  from  their  seats 
slightly  for  some  moments  to  permit  a  cir- 
culation to  become  established  before  the 
valves  are  fully  opened. 

When  the  boiler  is  in  service,  observe 
the  following  carefully  and  at  regular  in- 
tervals make  an  inspection  so  you  will  know 
everything  is  right. 


368   H.  P.  OF  STIRLING    BOILERS,   DOBCROSS   LOOM   WORKS,   DOBCROSS,  ENGLAND 

230 


TROUBLES    CAUSED    BY    OIL    IN    BOILERS 


231 


Steam  Gauges — When  pressure  is  off 
these  should  stand  at  zero,  and  when  safety 
valve  blows  off,  the  gauge  should  indicate 
the  same  pressure  for  which  the  valve  was  set 
to  pop.  If  it  does  not,  one  is  wrong,  and  the 
gauge  should  at  once  be  compared  with  one 
of  known  accuracy,  and  any  error  be  rectified. 

Safety  Valves — These  are  useless  if  al- 
lowed to  become  stuck  on  their  seats.  To 
prevent  this,  cause  the  valves  to  pop  once 
on  every  shift. 

Water  Level — Never  fire  a  boiler  with- 
out first  ascertaining  that  it  contains  the 
necessary  quantity  of  water.  When  operat- 
ing, never  depend  on  gauge  glass,  or  water 
alarms  alone,  but  try  the  gauge  cocks. 

Gauge  Cocks,  Water  Gauges,  and  pas- 
sages to  gauge  must  be  kept  clean,  and  should 
be  blown  out  frequently.  Formation  of 
colored  rings  on  the  glass,  due  to  oil  or  other 
deposits,  is  misleading,  and  should  be  ob- 
viated by  frequent  cleaning.  Automatic 
water  gauges  of  all  types  and  all  other 
automatic  appliances,  need  frequent  in- 
spection. 

Blow=Off  Valves  must  be  kept  tight,  and 
should  be  known  to  be  tight.  Every  blow- 
off  pipe  should  be  so  arranged  that  a  leak 
can  be  seen.  This  can  be  arranged  by  plac- 
ing in  the  pipe  just  beyond  the  blow-off 
valve,  a  tee  with  a  i"  outlet  to  which  a  gate 
valve  is  attached;  this  valve  should  be  left 
open  except  when  bio  wing-off  is  in  progress, 
so  that  it  will  act  as  a  tell-tale  in  case  the 
blow-off  is  leaking.  Where  boiler  water 
deposits  material  that  is  liable  to  cut  the 
blow-off  valve  and  cause  leaks,  a  gate  or 
asbestos  packed  plug  cock  should  be  placed 
between  boiler  and  regular  blow-off,  so  it 
can  be  closed  and  permit  the  blow-off  valve 
to  be  cleaned  without  shutting  dawn  the 
boiler. 

Firing — The  method  of  firing  coal  to  be 
adopted  will  depend  upon  the  kind  of  coal 
used;  the  chapter  on  Fuel  Burning  should 
therefore  be  carefully  studied,  and  the  most 
efficient  method  of  firing  be  determined  by 
close  observation  and  experiment.  The  draft 
should  be  regulated  to  the  least  amount 
necessary  to  maintain  the  desired  rate  of 
combustion. 

When  burning  wood,  carry  as  thick  a  fire 
as  the  draft  will  allow;  the  fresh  wood  on 


top  tends  to  force  down  the  partly  burned 
wood  thus  covering  the  grate  with  a  bed  of 
coals,  and  reducing  the  air  excess. 

When  burning  oil,  see  that  the  flame  is 
white,  not  red,  and  free  of  sparks  which 
indicate  incomplete  combustion.  The  air 
supply  should  be  regulated  to  a  point  where 
further  diminution  of  it  will  cause  smoke  to 
appear  in  the  stack.  Avoid  squirting  un- 
atoinized  oil  on  the  tubes  as  each  spot  where  it 
touches  is  liable  to  develop  a  blister. 

Foaming — If  caused  by  excessive  demand 
for  steam,  checking  the  outflow  of  steam  will 
usually  stop  it.  If  caused  by  excess  of  dirt 
due  to  concentration,  blowing  down  and 
pumping  in  clean  water  will  usually  stop  it. 
In  case  of  violent  foaming,  check  the  draft 
and  fires.  The  Stirling  boiler  never  foams 
with  good  water  unless  the  water  is  carried 
too  high,  in  which  case  lower  the  water-line, 
which  should  never  be  carried  higher  than 
two  gauges  when  the  boiler  is  steaming. 

Blowing  Off — When  feed  water  is  salty 
or  muddy,  blow  off  a  portion  at  as  frequent 
intervals  as  the  conditions  demand.  Empty 
the  boiler  every  week  or  two  and  fill  up 
afresh,  but  never  empty  the  boiler  while  brick- 
work is  hot,  and  never  feed  cold  water  into  a 
hot  boiler.  Always  blow  off  all  accumulations 
of  soot,  fuel,  etc.,  from  the  mud  drum  before 
emptying  a  boiler.  The  fine  coal,  particularly 
anthracite,  carried  over  on  the  drum  by  the 
draft,  may  hold  fire  many  hours  after  the 
furnace  fires  are  out.  If  under  such  con- 
ditions the  boiler  is  emptied  the  mud  drum 
and  tube  ends  may  be  overheated,  and  leaks 
or  broken  tubes  are  liable  to  result. 

Low  Water — Immediately  cover  fire  with 
ashes  or  earth,  preferably  wet;  in  default  of 
anything  else  handy  use  fresh  coal;  the 
important  point  is  to  check  the  heat  as 
quickly  as  possible.  Draw  the  fire  as  soon 
as  it  can  be  done  without  increasing  the  heat. 
Do  not  turn  on  the  feed,  lift  safety  valve,  start 
or  stop  engine,  until  boiler  is  cooled  down. 
Before  firing  the  boiler  again,  put  on  the  cold 
water  test,  locate  any  leaks,  and  stop  them. 

Cleaning — To  avoid  waste  of  fuel  and 
deterioration  of  the  boiler,  keep  it  clean  inside 
and  out,  by  carefully  following  the  directions 
given  in  chapter  on  Boiler  Cleaning. 

Oil  in  Boilers — Burnt  and  blistered  tubes 
will  be  the  inevitable  result  of  allowing  oil 


232 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


to  enter  boilers.  As  soon  as  the  presence  of 
oil  is  detected  the  boiler  should  be  cut  out  of 
service,  and  be  treated  as  directed  in  chapter 
on  Boiler  Cleaning. 

Air  Leaks— All  air  that  enters  boiler  or 
breeching  except  by  passing  through  the  fire, 
causes  losses  which  are  often  large  and  un- 
suspected. Carefully  test  for  leaks  around 
cleaning  door  frames,  blow-off  pipes,  dampers, 
breeching  connections,  etc.,  and  carefully 
plug  each  with  asbestos  rope  or  cement. 


use  unless  it  receives  proper  attention  as 
soon  as  its  use  is  discontinued,  hence  the  fol- 
lowing instructions  must  be  carefully  ob- 
served. Before  emptying  the  boiler  place 
in  each  upper  drum  several  gallons  of  crude 
oil  so  that  when  the  blow-off  is  opened  the  oil 
will  form  a  light  covering  over  the  inside 
surface  of  all  tubes  and  drums.  (Before  the 
boiler  is  started  again,  remove  this  oil  with 
soda-ash  as  already  directed.)  Dry  the 
boiler  thoroughly  when  emptied  out. 


STIRLING    CHAIN    GRATE   STOKERS   READY   FOR   SHIPMENT 


Steam  or  Water  Leaks  should  be  stopped 
without  delay,  and  extra  precaution  should 
be  taken  to  exclude  water  from  those  portions 
of  the  boiler  covered  by  brickwork,  other- 
wise unsuspected  corrosion  may  occur.  Leaks 
in  steam  pipes  over  the  boilers  should  be 
located  and  stopped. 

Internal  Corrosion  of  Boiler — This  is 
caused  by  some  harmful  agent  in  the  water, 
and  the  matter  should  at  once  be  referred  to 
some  competent  chemist  experienced  in  in- 
vestigating boiler  feed  water. 

Standing  Unused — If  a  boiler  remains  idle 
it  will  deteriorate  much  faster  than  when  in 


If  the  boiler  cannot  be  emptied,  fill  it  quite 
full  of  -water,  to  which  has  been  added  a 
quantity  of  soda-ash,  then  boil  off  the  air 
and  close  the  boiler  air-tight. 

Remove  the  baffle. tiles,  thoroughly  sweep 
off  all  accumulations  of  ashes  and  soot  with 
a  wire  brush,  and  give  all  tube  and  drum 
surfaces  a  coat  of  boiled  linseed  oil.  Smear 
all  brass  or  finished  work  with  vaseline  slush, 
or  a  mixture  of  white  lead  and  tallow. 

Cover  the  stack  tops  with  a  water  tight 
hood,  and  see  that  no  water  can  reach  the 
boiler  through  breechings,  openings  in  roof, 
or  other  sources. 


Specifications  for  Masonry  in  Stirling  Boiler  Settings 


To  secure  satisfactory  service  from  the 
boilers,  it  is  absolutely  essential  that  the 
setting  be  constructed  with  utmost  care, 
and  of  the  best  materials.  After  the  setting 
is  completed  it  should  be  carefully  dried 
out  as  directed  in  chapter  on  "Care  and 
Management  of  the  Stirling  Boiler"  (page  229) 
and  from  time  to  time  inspection  should  be 
made  to  locate  any  cracks  or  loose  brick- 
work, and  these  should  be  at  once  repaired. 
Prompt  attention  to  this  matter  will  not 
only  insure  more  efficient  results  from  the 
boiler,  but  obviate  unnecessary  repair  bills. 

The  following  specifications  should  be 
observed  during  progress  of  the  work: 

Excavation — Consult  the  drawings  and 
stake  off  accurately  according  to  dimensions 
given  thereon.  Where  boilers  rest  upon  rock, 
excavate  for  ash-pit  and  space  under  mud 
drum.  In  other  cases  excavate  to  depth 
shown  upon  drawing  or  to  such  additional 
depth  as  is  requisite  to  insure  a  solid  foun- 
dation. 

Concrete — Cover  the  entire  surface  with 
concrete  to  a  thickness  of  8  inches,  unless 
the  nature  of  the  soil  should  require  a  heavier 
bed.  When  found  necessary  do  not  hesitate 
to  make  the  bed  heavier.  The  composition 
of  the  concrete  should  be  one  yard  of  rock 
broken  to  pass  through  a  2-inch  ring,  \ 
yard  of  clean,  sharp  sand,  and  2\  barrels 
of  Portland  cement.  Clean  gravel  will  an- 
swer as  well  as  broken  rock.  Mix  well  when 
dry,  then  wet  and  mix  thoroughly.  Avoid 
using  too  much  water;  40  pounds  of  water 
to  each  100  pounds  of  cement  will  be  more 
than  ample.  When  placing  the  bed  of  con- 
crete on  foundation  cover  only  such  space 
as  the  quantity  mixed  will  bring  to  the  thick- 
ness required;  work  rapidly;  ram  the  con- 
crete well  with  a  50  Ib.  rammer  having  a  face 
8  inches  in  diameter,  and  continue  to  ram 
until  the  mass  is  so  compacted  that  water 
appears  on  the  surface.  See  that  the  bed 
of  concrete  is  level  and  smooth  when  finished. 

When  concrete  does  not  cost  more  than 
brickwork,  the  entire  foundation  up  to  floor 
line  is  frequently  made  of  concrete  with 
excellent  results. 


Red  Brickwork — Carefully  follow  the 
drawing  in  laying  off  the  brickwork  and  use 
good,  hard,  well  burned  brick,  uniform 
in  dimensions.  Wet  the  brick  before  laying. 
From  the  concrete  bed  to  the  floor  line  use 
a  well  mixed  mortar,  composed  of  one  part 
Portland  cement  to  two  parts  of  clean, 
sharp  sand,  grouting  each  course  thoroughly 
with  slush  mortar.  While  the  drawings 
show  a  cap  stone  under  each  support,  this 
is  imperative  only  where  the  brick  has  not 
a  crushing  resistance  equal  to  eight  times  the 
load  to  be  carried.  When  the  cap  stone  is 
omitted,  it  may  be  replaced  by  a  pier  made 
of  concrete,  or  of  selected  hard  brick  care- 
fully laid  in  Portland  cement  mortar. 

From  the  time  the  work  is  started  until 
the  last  brick  is  laid,  do  not  forget  the  im- 
portance of  tight  walls.  See  that  every 
brick  is  properly  bedded,  and  every  joint 
well  and  thoroughly  filled  with  mortar. 
Air  leaks  through  the  walls  ruin  the  draft 
and  destroy  the  efficiency  of  the  boiler. 

All  walls  must  be  built  straight  and  plumb, 
and  carried  up  simultaneously,  thoroughly 
grouting  each  course. 

On  all  red  brickwork,  from  the  floor  line 
up,  use  well  mixed  mortar,  composed  of  one 
part  lime  to  three  parts  clean,  sharp  sand. 
Mortar  must  not  be  used  while  hot,  caused 
from  the  slacking  of  freshly  burned  lime. 

The  brick  should  be  laid  in  courses  of 
four  stretchers  to  one  header,  i.  e.,  every 
fifth  course  should  be  a  header  course. 

As  the  work  progresses,  see  that  all  stay 
rods  and  anchor  bolts  are  properly  placed; 
set  and  anchor  all  door  frames  as  shown  on 
drawing,  turning  over  each  door  an  arch 
extending  through  the  thickness  of  the  wall. 
See  that  there  are  no  air  leaks  between  the 
door  frames  and  the  brickwork. 

The  mud  drum  must  be  perfectly  free,  to 
allow  the  tubes  to  expand  and  contract  as 
the  conditions  may  require,  and  at  no  place 
must  the  brickwork  be  allowed  to  touch 
either  the  mud  drum  or  the  blow-off  pipe. 
This  rule  positively  admits  of  no  exception. 
Nothing  must  affect  the  freedom  of  the  mud 
drum.  At  the  manhole  end  of  mud  drum 


o      - 


PROPERTIES    OF    FIRE-CLAY 


235 


turn  a  complete  arch  circle,  the  inside  of 
the  circle  being  kept  i-inch  clear  of  the 
drum.  This  space  to  be  afterwards  filled 
with  a  ring  of  i-inch  asbestos  rope.  Before 
the  blow-off  valve  is  attached,  slip  over 
blow-off  pipe  a  piece  of  4-inch  pipe  12  inches 
long,  and  build  same  into  wall  as  a  thimble 
through  which  blow-off  pipe  passes,  then  plug 
up  the  annular  space  between  the  two  pipes 
with  asbestos  rope  or  fiber. 

The  bridge  wall  must  be  carefully  laid  to 
allow  the  mud  drum  freedom.  There  must 
be  a  space  of  i^  inches  between  the  top  of  the 
bridge  wall  and  the  front  row  of  tubes. 

In  laying  the  red  brick  on  top  of  the 
steam  drums  and  the  steam  circulating 
tubes,  use  every  precaution  to  have  tight 
joints  so  as  to  thoroughly  exclude  air  leaks. 
These  bricks  are  to  be  laid  in  lime  mortar, 
with  the  joints  open  at  the  upper  edge,  and, 
after  all  the  bricks  are  in  place,  these  joints 
should  be  slushed  with  cement,  leaving  a 
covering  on  top  of  the  brick  at  least  ^-inch 
thick.  The  thinner  the  joints  between  the 
bricks  the  longer  the  setting  will  last. 

Fitting  Brickwork  Around  Boiler  Sup= 
ports  —  Figs.  No.  50  to  57  show  how  this 
should  be  done.  The  red  bricks  should  be 
laid  up  close  against  the  inside  flange  of  the 
outer  columns  as  shown  in  Figs.  No.  50 
and  51.  Along  the  rear  side  of  the  front 
column,  and  the  front  side  of  the  rear  column, 
the  face  of  the  brickwork  should  be  in  line 
with  the  outer  edge  of  the  flanges  of  the 
I-beam  column,  with  the  exception  that  every 
fifth  course  of  bricks  should  be  placed  into 
contact  with  the  web  of  the  columns,  as 
marked  in  Fig.  51. 

When  two  boilers  are  set  in  battery  there 
will  be  three  angle-iron  columns  placed  in- 
side of  the  party  wall,  and  all  around  these 
columns  a  clearance  of  one-half  inch  must 
be  left  between  them  and  the  brickwork, 
as  shown  in  Figs.  52,  53,  and  54. 

When  building  the  brickwork  behind  the 
metal  front  of  the  boiler  care  must  be  taken 
to  see  that  it  is  placed  in  exact  accordance 
with  Fig.  55.  The  outer  course  of  the  side 
walls  should  be  carried  up  to,  and  closely 
fitted  against,  the  inside  of  the  face  of  the 
outer  columns  and  pilasters,  so  that  the  flange 
of  the  pilaster  or  column  overlaps  the  side 
wall  as  shown  in  Fig.  56.  The  remainder 


of  the  brickwork  behind  the  metal  front 
should  be  carried  up  so  that  its  forward  face 
is  one  inch  behind  the  panel  plates,  with  the 
exception  that  each  fifth  course  of  brick 
should  project  forward  sufficiently  to  come 
into  contact  with  the  metal  front,  thus  as- 
sisting in  supporting  it  and  in  holding  the 
panel  plates  securely  in  place,  as  illustrated 
in  Fig.  55. 

In  order  that  the  brickwork  may  be  per- 
fectly tied  or  bonded,  the  header  courses 
on  the  inside  and  outside  faces  of  the  wall 
should  be  on  the  same  level  and  abut  each 
other  in  the  center  of  the  wall;  a  course  of 
headers  must  also  be  placed  inside  of  the 
wall  both  above  and  below  the  outside 
header  courses,  and  across  their  abutting 
line,  as  in  Fig.  57. 

Lime  Mortar — Lime  is  greatly  improved 
by  allowing  it  to  stand  as  long  as  possible 
between  time  of  slacking,  and  using  in  the 
wall.  In  some  countries  lime  is  slacked  and 
allowed  to  remain  in  pits  a  year  before  using, 
as  the  first  slacking  is  not  complete,  and 
the  mass  contains  small  particles  which  slack 
only  after  long  standing.  When  freshly 
slacked  lime  is  used  in  a  boiler  setting,  these 
unslacked  particles  finally  swell,  the  mortar 
gets  loose  and  "shattered,"  and  the  brick- 
work is  a  failure.  Lime  for  boiler  setting 
should  be  slacked  at  least  six  weeks,  or  longer 
if  possible,  before  using. 

Fire=Clay — Fire-clay  is  not  a  cement, 
and  it  has  little  or  no  holding  power.  Its 
office  is  therefore  not  to  act  as  a  binder,  but 
merely  to  fill  the  voids.  In  consequence  a 
fire-brick  joint  is  the  more  perfect  in  pro- 
portion as  the  quantity  of  fire-clay  ap- 
proaches the  amount  necessary  to  fill  the 
voids,  without  preventing  the  brick  from 
touching,  precisely  as  in  case  of  a  glue  joint 
between  pieces  of  wood.  Clay  of  consistency 
sufficient  to  permit  use  of  trowel  should  not 
be  permitted;  the  proper  way  is  to  mix  the 
clay  to  requisite  thinness,  dip  each  brick 
into  the  clay,  "rub  and  shove"  each  brick 
into  final  place,  then  drive  it  with  mallet 
or  hammer  and  block,  until  it  actually 
touches  the  brick  below  it.  Rigid  adherence 
to  these  directions  is  absolutely  essential  when 
constructing  -fire-arches. 

The  two  defects  of  fire-clay  are  its  shrink- 
age during  drying,  and  its  lack  of  cement- 


236 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


ing  power.  The  former  may  be  greatly 
diminished  by  adding  to  the  clay  about  20 
per  cent,  of  its  volume  of  fire-brick  pulverized 
and  sifted  to  fire-brick  flour.  This  can  be 
obtained  in  many  places,  but  unless  it  is 
of  the  requisite  fineness,  avoid  it,  as  coarse 
material  will  thicken  the  joints  an  amount 
which  offsets  the  advantage. 

The  cementing  power  of  fire-clay  may  be 
increased  by  adding  to  and  slacking .  in  with 
it  about  i^  per  cent,  of  its  volume  of  lime; 
measure  the  clay  and  for  each  cubic  foot,  put 
in  a  piece  of  lime  not  exceeding  4X2X2^ 
inches.  This  will  have  just  sufficient  fluxing 
power  to  unite  with  the  clay  and  form  a  hard 
clinker  which  takes  a  grip  on  the  fire-brick. 
It  should  always  be  used  when  building 
arches. 


measurements  carefully,  and  lay  off  the 
lines  of  the  skewback.  When  determining 
length  of  arch,  be  sure  to  consult  the  draw- 
ing for  the  particular  job  on  which  you  are 
working,  as  the  arch  length  varies  with 
character  of  fuel.  While  laying  off  the  skew- 
back,  and  while  laying  the  brick  in  same, 
use  a  true  straight  edge  the  length  of  the 
arch.  See  particularly  that  the  skewbacks 
have  no  lumps,  bumps  or  other  irregular- 
ities and  the  brick  wall  behind  them  is 
absolutely  solid,  and  the  red  bricks  laid  close 
together  so  there  will  be  no  space  filled  with 
mortar  or  spalls.  See  that  the  two  skew- 
backs  are  perfectly  parallel,  level  and  in 
line,  the  one  with  the  other.  Keep  using 
the  straight  edge  until  the  surfaces  are  smooth 
and  regular. 


PLAN  OF  ARCHES 


SKEW  BACKS  TO  BE  ALL 
FIRE  BRICK,  LAID  CLOSE 
AVOID  SPALLS  OR  MORTAR 
FILLING. 

W  WEDGE  BRICK 
S=SQUARE  BRICK 


FIG.  58 


DETAILS   OF  FURNACE  ARCHES 


FIG.  59 


Fire=Brick  Work — When  the  point  in 
the  brickwork  has  been  reached  where 
the  fire-brick  commences,  the  fire  and  red 
brick  must  be  carried  up  together,  and  from 
a  distance  6  inches  below  the  bottom  of  the 
grate  bars  to  the  skewback  of  the  arch,  every 
course  must  be  a  header  course,  and  every 
fifth  course  of  the  fire-brick  must  be  tied 
into  the  red  brick.  The  best  fire-brick 
obtainable  must  be  used  in  the  side  walls 
of  the  furnaces  and  arches,  beginning 6  inches 
below  the  bottom  of  the  grate  bars,  and 
carried  up  on  both  side  walls  to  the  top  of 
the  arch,  and  from  the  front  wall  back  to 
the  front  baffle-tiling.  The  arches  must  be 
constructed  also  of  the  very  best  grade  of 
fire-brick  obtainable.  All  fire-brick  must 
be  closely  laid  with  a  solution  of  fire-clay 
and  water  as  above  directed. 

Fire=Arches — When  the  arch  above  the 
fire  is  reached,  consult  the  drawing,  take 


Next,  set  the  center  upon  which  the  arch 
is  to  be  turned  and  make  the  center  as  fol- 
lows :  cut  from  i  £-inch  plank  three  seg- 
ments of  the  proper  length  and  radius.  Let 
the  distance  between  the  two  outer  segments 
be  6  inches  less  than  the  length  of  the  arch; 
place  the  third  segment  in  the  center  of  the 
two  outer  ones.  See  that  they  are  parallel 
with  each  other  and  square,  so  that  there 
will  be  no  wind  in  the  center  when  nailed  up. 
Batten  the  segments  with  i-inch  square 
strips,  laid  close  together,  said  strips  being 
smooth  and  straight. 

After  the  strips  are  well  and  securely 
nailed  to  segments,  plane  off  to  a  true  circle. 
When  the  center  is  completed,  set  in  place, 
being  careful  that  the  two  outside  strips 
line  exactly  with  skewbacks.  If  they  will 
not  line,  either  the  skewbacks  or  center 
must  be  wrong,  and  the  defective  one  should 
be  righted  before  a  single  brick  is  laid. 


LOCATING    THE    BAFFLING    TILES 


137 


When  the  center  is  set  and  found  right, 
select  smooth,  straight  and  uniform  rectan- 
gular bricks  and  wedge  bricks  (bull  heads); 
have  the  solution  of  fire-clay  soft  and  well 
mixed.  Do  not  use  a  trowel;  dip  the  bricks 
and  shove  up  close,  driving  to  place  with  a 
brick  hammer,  or  mallet  and  block. 

Keep  the  joints  as  thin  as  possible. 

The  bricks  must  positively  not  be  laid  in 
consecutive  rings;  every  joint  must  be 
broken  and  have  a  bond  equal  to  one-half  the 
width  of  a  brick.  While  laying  the  arch, 
alternate  square  brick  with  bull  heads  and 
vice  versa,  as  may  be  found  necessary  to 


show  the  smallest  and  largest  arches,  the 
same  general  plan  of  procedure  covers  all 
intermediate  sizes. 

Finally,  at  end  of  arch,  run  a  g-inch  wall 
across  the  spandrel  openings,  as  at  A,  Fig.  59, 
to  provide  a  parallel  throat  for  gases  as  they 
pass  into  the  tubes. 

Fire  Door  Arches — For  building  the  fire 
door  arch  The  Stirling  Company  furnishes- 
a  special  skewback.  Consult  the  draw- 
ing, and  the  accompanying  cuts,  Figure  60, 
and  follow  them  closely,  using  the  same 
careful  methods  advised  in  building  the  fire- 
arches.  The  bricks  (bull  heads)  in  this  arch 


ELEVATION  OF  ARCH  NO.   1 


ELEVATION 


SECTIONAL  ELEVATION 


SECTIONAL  PLAN 


SKEW  BACK 


FIG.  60.     DETAILS   OF  FIRE    DOOR   ARCHES 


maintain  a  true  circle.  Be  particularly 
careful  that  the  arch  is  not  turning  too  fast. 
When  the  keying  course  is  reached,  try  the 
bricks  in  dry  and  see  that  they  have  the 
proper  taper.  If  not  of  the  proper  taper 
cut  them  nicely  to  fill  the  space. 

Do  not  leave  any  interstices  to  be  filled 
with  fire-clay,  as  it  will  only  fall  out  when 
dry  and  let  the  arch  down. 

The  keying  course  should  be  a  snug  fit, 
driven  carefully  to  place  by  laying  a  small 
block  of  wood  on  top  of  the  brick,  on  which 
hammer  lightly,  being  careful  not  to  drive 
so  hard  as  to  crush  or  otherwise  mutilate 
the  brick.  When  properly  keyed,  remove 
the  center. 

Figures  58  and  59  fully  illustrate  how 
this  arch  should  be  built.  While  the  figures 


must  be  turned  in  consecutive  rings,  making 
no  attempt  to  bond  the  one  with  the  other. 

The  fire  bricks  laid  above  the  water  circu- 
lating tubes  must  not  be  laid  tight  nor  keyed 
like  an  arch.  Dip  the  bricks  in  fire-clay  and 
lay  snugly  to  place;  when  completed  grout 
with  fire-clay  wash,  leaving  a  good  coating 
above  the  bricks. 

Baffling  Tile — Consult  the  drawing  and 
see  that  all  supports  and  hangers  for  the 
baffling  tiles  are  in  proper  place.  If  found 
wrong  have  them  righted  before  laying  a 
single  tile.  Commence  at  the  side  wall  and 
lay  the  tiles  in  rows  longitudinally  with  the 
drums,  laying  a  single  row  at  a  time. 

See  that  the  first  tile  fits  smoothly  and 
closely  to  the  side  wall,  and  that  the  other 
edge  comes  immediately  back  of  the  vertical 


238 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


center  of  the  tube.  If  found  too  wide,  cut 
to  fit.  Care  at  this  point  will  bring  every 
seam  in  the  row  exactly  back  of  the  tube 
centers.  Fit  the  entire  row  dry,  and  see 
that  each  tile  lies  closely  and  snugly  to  its 
companion. 


Follow  all  these  instructions  until  all  the 
tiles  are  laid,  watching  that  the  tiles  fit 
closely  at  the  joints,  top,  bottom  and  sides. 
See  that  there  are  no  bumps  on  the  portion  of 
the  tile  face  that  comes  into  contact  with  the 
tubes;  let  it  lie  smoothly  and  evenly  in  place. 


PART   OF    1,500    H.   P.   OF   STIRLING    BOILERS,  WOLVERINE   COPPER    MINING    CO,   KEARSARGE,    MICH. 


Here  also,  the  trowel  must  be  set  to  one 
side.  Dip  the  edges  of  the  tiles  in  a  fire-clay 
solution,  then  lay  them  into  place  carefully. 

There  must  be  no  leaks  in  joints  nor  stop- 
ping up  of  interstices  with  fire-clay  to  fall 
out  when  dry,  and  thus  divert  the  gases  from 
their  proper  course,  allowing  them  to  take 
short  cuts  to  the  smokestack. 


After  all  is  done,  give  the  joints  several 
coats  of  clay  wash  which  should  be  made 
of  a  thin  solution  of  fire-clay,  and  be  applied 
with  a  whitewash  brush. 

All  cleaning  doors  are  to  be  located  in 
side  and  rear  walls  as  shown  on  blue  prints; 
fit  the  brick  close  up  against  the  door  frames 
to  prevent  air  leakage. 


Index 


The  figures  refer  to  the  pages. 


Absolute  pressure,  definition,  72;  of  steam, 

71.   72-  74- 

Absolute  temperature,  48. 

Absolute  zero,   48. 

Acids,  cause  pitting  and  corrosion,  61 ;  method 
of  neutralizing,  61 ;  sources  of  in  feed  water, 
6 1 ;  testing  for  in  kerosene,  228. 

Acetylene,   weight   and   calorific   value,    133. 

Adaptability,  the  comparative  of  different 
types  of  boiler  to  various  duties,  41. 

Air,  chapter  on,  55  ;  composition  of,  55 ;  causes 
corrosion  of  boilers  when  dissolved  in  feed 
water,  61 ;  cooling  effect  of  excess  of,  table, 
1 08;  filters  through  leaks  in  boiler  settings, 
232;  specific  heat  of,  55;  weight  of  required 
for  combustion,  106,  table,  107;  formula 
for  pressure  and  volume  of,  55;  weight 
and  volume  of,  table,  55;  vapor  in,  55,  56. 

Alabama  coals,  analyses  and  heating  value 
of,  116;  proximate  and  ultimate  analyses 

of,   i35- 

Alabama  Steel  and  Wire  Co.,  boilers  of,  140. 

Altitude,  atmospheric  pressure  correspond- 
ing to,  58;  determination  of  stack  dimen- 
sions according  to,  176;  effect  of  on  boiling 
point  of  water,  58. 

American  coals,  analyses  and  calorific  value 
of,  1 14. 

American  Society  of  Mechanical  Engineers' 
code  of  rules  for  boiler  trials,  201. 

Anaconda  Copper  Mining  Co.,  boilers  of,  212. 

Analyses,  caution  in  interpreting,  131;  cal- 
culation of  heat  value  from,  106,  131,  and 
135  to  138;  of  flue-gases,  181;  proximate, 
131,  135;  ultimate,  131. 

Analysis  of  coal  for  boiler  tests,  205. 

Anthracite,  analyses  of,  in,  114;  chemical 
changes  from  wood  into,  in;  calorific 
value  of,  112,  114;  description  and  market 
sizes  of,  in;  fixed  carbon  and  volatile 
matter  in,  in,  112;  may  hold  fire  many 
hours,  231;  methods  of  burning,  141. 

Atmosphere,  flow  of  steam  into,  90  and  91; 
Napier's  formula  for  flow  of  steam  into, 
91 ;  pressure  per  square  inch  of,  at  different 
altitudes,  58. 

Atomic  weight  of  elements  affecting  com- 
bustion, 105. 


Arch  bars  of  the  Stirling  boiler,  9,  15. 
Arches,  construction  of  for  furnaces  and  fire 

doors,    236,    237;    necessary    over    furnaces 

for  good  combustion,   142. 
Armour  Institute,  boilers  of,  40. 
Ash,  composition  of,  112. 
Ashes  and  refuse,  treatment  of  during  boiler 

test,  204. 

Ash-pit  doors  of  the  Stirling  boiler,  17. 
Automatic  furnace  feeder  for  bagasse,    148. 
Automatic  stop  valves  for  boilers,   169,  173. 
Available  draft  in  stacks,  217. 

.Baffles,  in  the  Stirling  boiler,  n;  effect  of 
tubes  passing  through,  n;  tiles  for,  and 
how  they  should  be  laid,  237. 

Bagasse,  description  and  calorific  value,  120, 
12 1 ;  conveyor  and  automatic  feeder  for, 
148;  effect  of  moisture  in,  147;  furnace  and 
setting  of  Stirling  boiler  for  burning,  146, 
147  ;  test  of  boiler  burning,  149. 

B amis'  draft  gauge,  179. 

Beaume's   hydrometer  for  testing  oils,    126. 

Benzine,  123. 

Bernoulli's  theorem,  87. 

Berwind  White  Coal  Mining  Co.,  boilers 
of,  20. 

Bingham  Copper  and  Gold  Mining  Co.,  boilers 
of,  194. 

Bituminous  coal,  analyses  of,  in,  115; 
behavior  of  in  furnaces,  142;  description 
and  general  properties,  in;  heat  value  of, 
112,  115;  fixed  carbon  and  volatile  matter 
in,  in,  112;  injured  by  exposure  to  weather, 
113;  methods  of  burning,  142. 

Block-Pollack  Iron  Co.,  boilers  of,  166. 

Blast  Furnace  gas,  boiler  for  utilizing,  164; 
burning  of,  163;  computation  of  heating 
value  of,  133;  test  of  boiler  burning,  165. 

Bio  wing-off,  with  salt  or  muddy  water,  231. 

Blow-off  valves,  231. 

Boilers,  adaptability  of  different  types  to 
different  requirements,  41 ;  cleaning  of, 
223;  chart  representing  efficiencies  of,  188; 
code  of  rules  for  trials  of,  201 ;  covering  for, 
219;  distribution  of  heat  developed  in  fur- 
naces of,  191 ;  effect  of  oil  in,  231 ;  efficiency 
of,  29,  39,  126,  127,  153,  187,  205;  for  min- 


MILLS    BUILDING,  SAN    FRANCISCO,  CAL.,  OPERATING  450    H.  P.  OF  STIRLING    BOILERS 


ur     I  n  r 


INDEX 


241 


ing  service,  209;  horse-power  of,  195  et  seq.; 

preparation   of,   for   standing  unused,    232; 

provision    for    overload    capacity    in,    199; 

selection   of,    for   a   given   engine   capacity, 

195;  Scotch  Marine  boiler,  37;  the  Stirling 

boiler,  see  Stirling  boiler;  water-tube  versus 

fire-tube  boilers,  35. 
Boiler  feed  water,  see  feed  water. 
Boiling  points,  of  water  at  different  altitudes, 

58;  of  sea  water,   58;  table  of,  for  various 

substances,  49. 

Bolts  for  steam  pipe  flanges,  table,  217. 
Brickv/ork,  specifications  for,  233. 
British  thermal  unit,  48. 
Brownlee's  table  for  flow  of  steam,  91. 
Brail's  experiments  on  constriction  of  circu- 
lation in  horizontal  water- tube  boilers,   15. 
Burners  for  petroleum,  152;  number  required 

for  different  furnace  widths,  153;  per  cent. 

of  steam  used  by,  153 ;  pressure  of  oil  needed 

for,  153. 

(Baking  and  non-caking  coals,    in. 

California  oils,  heat  value  of,  125. 

Calorimetry,  of  fuels,  138;  as  applied  in 
determining  specific  heat  of  solids,  55. 

Calorimeters  for  fuel,  Mahler's,  138;  Parr's, 
138. 

Calorimeters  for  steam,  chart  for  use  with, 
80;  compact  form  of,  83;  formulas  for,  81, 
85;  limits  of  accuracy  of  throttling,  83; 
location  of  sampling  nipple  for,  85,  204; 
separating,  83;  sources  of  error  in,  81; 
taking  an  observation  with,  85;  throttling, 
and  equations  for,  79. 

Calorific  value,  see  heat  value. 

Calorie,  48,  131,  foot-note. 

Candler  building,  boilers  of,  224. 

Cannel  coal,  112. 

Capital  invested,  efficiency  of,  31. 

Carbon  monoxide,  heat  loss  due  to  incom- 
plete combustion  of,  191;  weight  and  heat 
value  of,  133. 

Carbon,  atomic  weight  of,  12;  combustion 
data  for,  106;  fixed,  112. 

Care  and  management  of  boilers,  229. 

Cast  iron,  why  first  used  in  manufacturing 
water-tube  boilers,  7 ;  elimination  of  from 
the  Stirling  boiler,  17;  is  a  cause  of  boiler 
explosions,  17;  trade  names  under  which  it 
is  often  disguised,  17. 

Caustic  potash  for  Orsat  apparatus.  184. 

Caution  in  interpreting  analyses,  of  fuels,  131. 


Chain  grate  stokers,  effect  of  excess  air  in 
connection  with,  145;  the  Stirling  chain 
grate,  159. 

Charts,  showing  boiler  efficiency,  188;  show- 
ing combustion  rate  of  coal,  189;  showing 
ing  diameter  and  horse-power  of  chimneys, 
172;  showing  draft  required  for  different 
coals,  174;  showing  graphical  representa- 
tion of  Kent's  heating  values  in  terms  of 
combustible,  137;  for  Goutal's  fuel  formula, 
136;  for  Mahler's  fuel  formula,  132;  show- 
ing relation  between  gas  temperature,  steam 
generated,  and  heating  surface  passed  over, 
94;  for  throttling  calorimeter,  80. 

Check  valve  in  drain  pipe,  215. 

Chemical    elements,    combining    weights    of, 

105- 

Cheval,  definition  and  value  of,  195. 

Chicago  Union  Traction  Co.,  boilers  of,   22. 

Chimneys  and  draft,  chapter  on,  169. 

Chimneys,  draft  in  one  100  feet  high,  169; 
draft  losses  in,  171,  173;  height  and  diameter, 
173;  horse-power  of,  172;  Kent's  table  of, 
177;  proportions  of,  for  boilers  burning  oil, 
178;  proportions  of,  for  high  altitudes,  176; 
solution  of  a  typical  problem  in  the  design 
of,  176. 

Cincinnati  Gas  and  Electric  Co.,  boilers 
of,  14. 

Circular  drum  seams  eliminated  from  the 
Stirling  boiler,  8. 

Circulation  of  water,  constriction  of  obviated 
in  the  Stirling  boiler,  15;  M.  Brail's  ex- 
periments on,  15. 

Classification  of  coals  according  to  com- 
bustible, in. 

Classification  of  good  and  bad  feed  water,  65. 

Cleaning  of  boilers,  chapter  on,  223;  com- 
parison of  the  difficulty  of,  for  various 
types,  39;  on  fire  side  of  heating  surface, 
23,  228;  on  interior  of  heating  surface,  21, 
223. 

Cleaning    doors    of    the    Stirling    boiler,    n. 

Coal,  analyses  of  Alabama,  135;  analyses 
and  calorific  value  of  leading  American, 
114;  approximate  heating  value  of  general 
grades,  112;  ash  in,  112;  bituminous,  de- 
scription of,  in;  behavior  of  in  furnace, 
142;  caking  and  non-caking,  in;  cannel, 
112;  classification  of  according  to  com- 
bustible, in;  compared  with  natural  gas, 
129;  compared  with  petroleum,  126;  defini- 
tion of  kinds,  in;  description  and  sizes 


242 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


of  anthracite,  1 1 1 ;  determination  of  moisture 
in,  204;  draft  required  for  different  kinds, 
113;  dust,  burning  of,  113;  Hunt's  formula 
for  heat  value  of  Illinois,  136;  Kent's  table 
of  approximate  heat  values  of,  135,  and 
chart,  137;  methods  of  firing  various  kinds 
of,  143;  sampling  of,  204;  semi-anthracite, 
in;  semi-bituminous,  in;  tables,  112,  114 
to  1 1 8 ;  weathering  of,  113;  weight  of  burned 
per  square  foot  of  grate  at  different  boiler 
ratings,  191,  and  chart,  189. 

Coal  tar,  129. 

Coke,  119. 

Coke  ovens,  utilization  of  waste  heat  from, 
161;  boilers  for  burning  gases  from,  162; 
test  of  boiler  burning  gases  from,  163. 

Colorado  Fuel  and  Iron  Co.,  boilers  of,   12. 

Columbia  Chemical  Co.,  boilers  of,  16. 

Combining  weights  of  chemical  elements,  105. 

Combustible,  classification  of  coals  according 
to,  in;  does  not  really  include  oxygen 
and  nitrogen,  112,  foot-note. 

Combustion,  air  required  for,  106,  107,  183; 
chapter  on,  105;  chart  showing  draft  re- 
quired for  various  rates  of  for  various  coals, 
174;  hydrogen  available  for,  106;  rates  of, 
at  different  boiler  capacities,  chart,  189; 
ratio  of  air  supplied  to  theoretical  amount 
required  for,  183,  184. 

Commercial  efficiency  of  boilers,  29. 

Compressibility  of  water,  57. 

Concrete,  composition  and  working  of,  233. 

Consolidated  Main  Reef  Mines  and  Estates, 
boilers  of,  78. 

Constriction  of  circulation  in  boilers,  causes 
steam  pockets  and  reversal  of  direction  of 
flow,  15;  obviated  in  the  Stirling  boiler,  15. 

Construction  of  the  Stirling  boiler,  advan- 
tages of,  11,  23;  imitations  of,  33. 

Contraction  and  expansion  fully  provided  for 
in  Stirling  boilers,  13. 

Convection  of  heat,  50. 

Cooling  effect  of  excess  air  in  boiler  fur- 
naces, 108. 

Copper  Queen  Consolidated  Mining  Co., 
boilers  of,  170. 

Correction  for  heat  values,  on  account  of 
hydrogen,  moisture  and  nitrogen,  133. 

Corrosion  of  boilers,  61,  232;  Ost's  theory 
of,  61. 

Cotton  States  and  International  Exposition, 
boilers  of,  199. 

Counterbalanced  fire  doors,  31. 


Course  of  gases  in  the  Stirling  boiler,  1 1. 
Coverings  for  boilers  and  pipes,  219. 
Cuprous  chloride  for  Orsat  apparatus,    184. 
Curved  tubes,  advantages  of,  and  unfounded 

prejudice  against,  21. 
Cutters  for  turbine  tube  cleaner,  226. 
Cutting  boiler  into  steam  main,  229. 
Cylinder  boilers,  waste  heat  from,  167. 

Data  and  results  of  evaporative  tests,  206; 

same  worked  out  for  a  specific  case,  192. 
Density,   of  gases   at   atmospheric  "pressure, 

182 ;  of  mixtures  of  air  and  vapor,  56. 
Determination  of  heating  value  of  fuels,  131. 
Detroit  Edison  Company,  boilers  of,  96. 
Diagrams  of  steam  pipe  systems,  214. 
Diffusion  bagasse,  121,  122. 
Distribution   of   heat   losses   in   boilers,    191. 
Dobcross  Loom  Works,  boilers  of,  238. 
Draft,     available,     169,     173;    for    different 

fuels,   174,   175;  formula  and  constants  for, 

171;  in  chimney  100  feet  high,   169;  losses 

of    in    furnaces    and    flues,    175;    losses    in 

stacks,    171;    must    be    regulated    for   each 

fuel   and   combustion   rate,    141.     Also   see 

chimneys  and  draft. 
Draft  gauges,  178. 
Drain    pipes    for    steam    mains,    215;    check 

valve  in,  215. 

Drilling  templet  for  steam  pipe  flanges,  217. 
Driving   boilers    at    high    and    low    rates    of 

evaporation,  27. 
Drums,   absence   of  complication   in,   of  the 

Stirling  boiler,  13;  for  steam  storage,  proper 

location  for,  209,  211,  216. 
Drum  heads  of  forged  steel,  9,13. 
Drum  lugs  of  the  Stirling  boiler,  15. 
Dry    steam,    production    of    in    the    Stirling 

boiler,  27. 

Dulong's  fuel  formula,  106,  131. 
Duplicate  steam  pipe  systems,  216. 
Durability  of  the  Stirling  boiler,  23. 
Dust  from  coal,  utilization  of,  113. 

rLbullition,  49. 

Economizers,  67. 

Economy  of  high  pressure  steam,  73. 

Edison  Electric  Co.,  Los  Angeles,  boilers 
of,  98. 

Effect  of  and  correctives  for  impurities  in 
feed  water,  59. 

Efficiency,  of  boiler  and  grates,  187;  calcula- 
tion of  for  boilers,  205;  chart  of,  188;  191; 


INDEX 


243 


of  fuel,  29;  of  capital  invested,  29;  of  ideal 
perfect  heat  engine,  73;  obtainable  from  oil, 
153;  relative,  of  boilers  when  clean  and 
foul,  39;  variation  of,  at  different  rates  of 
driving,  193. 

Elbows    in    steam    pipes,    resistance    of,    89. 

Elimination  of  temperature  stresses  from 
the  Stirling  boiler,  37. 

Ellison's  draft  gauge,  179. 

Energy  stored  in  steam  boilers,  17. 

Engines,  consumption  of  steam  for  different 
types  of,  198;  efficiency  of  ideal  perfect,  73; 
hoisting,  and  boilers  for  operating  them, 
209;  selection  of  boilers  for  operating  a 
given  power  of,  195. 

Equivalent  evaporation  from  and  at  212 
degrees,  69. 

Ethane,  weight  and  heat  value  of,  133. 

Evaporation,  driving  boilers  at  high  and 
low  rates  of,  27;  factors  of,  70,  71;  from 
and  at  212  degrees,  69;  required  amount 
per  hour  per  boiler  horse-power  from  differ- 
ent feed  temperatures,  198;  total  heat  of,  50; 
units  of,  72. 

Excess  air  in  furnaces,  effect  of,  108. 

Expansion,  coefficients  of  linear,  51;  and 
contraction,  fully  provided  for  in  the  Stirling 
boiler,  13. 

Explosion  of  tubular  boilers,  36,  37. 

r  actors  of  evaporation,  70. 

Feed  valve  for  boilers,  should  always  be  a 
globe,  217. 

Feed  water,  chapter  on,  59;  classification  of 
good  and  bad,  65;  effect  of  and  correctives 
for  impurities  in,  59;  heating  of,  63,  67; 
operation  of  Stirling  boilers  when  fed  with, 
19;  purification  of  by  chemicals,  61;  re- 
agents for  treating  after  it  enters  boiler, 
63;  scale-forming  materials  in,  59. 

Fire,  temperature  of,  table,  50;  computa- 
tion of  temperature  of,  107. 

Firing,  methods  of  for  boilers,  143,  231. 

Fire-brick,  arches  of  over  furnaces  necessary 
for  good  combustion,  142;  directions  for 
laying,  236;  damage  to,  caused  by  admitting 
cold  air  into  furnaces,  223. 

Fire-clay,  properties  and  preparation  of,  235. 

Fire  doors,  construction  of  arches  over,  237; 
counter  balanced,  31;  of  the  Stirling  boiler, 

17- 

Fire-tube  versus  water-tube  boilers,  35. 
First  National  Bank  building,  boilers  of,  218. 


Flanges  for  steam  pipe,  dimensions  and  drill- 
ing templet  of,  217. 

Flash  point  of  oils,  125. 

Flow  of  steam,  chapter  on,  87;  into  the  at- 
mosphere, 90,  91;  Napier's  formula  for,  91; 
through  pipes,  87,  89. 

Flowed  steel,  a  trade  name  for  cast  iron,  17. 

Flues,  draft  losses  in,  175;  effect  of  right- 
angled  turns  in,  175;  proper  area  of,  175; 
for  boilers  burning  oil,  178. 

Flue-gas,  analysis  of,  181,  205;  formula  for 
weight  of.  183;  heat  carried  off  by,  183; 
object  of  analysis  of,  181;  Orsat  apparatus 
for  analysis  of,  and  solutions  for,  184; 
table  of  results  from  analysis  of,  186. 

Foaming  in  boilers,  causes  and  remedies,  65, 
231;  due  to  carbonates,  60;  due  to  feeding 
cold  water  68;  due  to  grease,  64;  due  to 
scum,  60. 

Ford  Plate  Glass  Co.,  boilers  of,  38. 

Formulas  in  this  book: 

No.       PAGE     No.         PAGE     No.         PAGE 

i 53      20 89      38 173 

2 55      21 89      39 173 

3-  •          58      22.         .91      40 173 

4-  67      23.  ...    91      41 173 

5 72  j  106      42 175 

6..      .    81  (  131      43-.       -183 

7  .....    81      25 107      44 183 

8 81      26 107      45 183 

9 85      27 121      46 183 

10 87      28 123      47.         .  183 

ii 87      29. ....131      48 183 

12. .          .87        30. .. .131        49. .         . 183 

13-  -      -   •     87        31.   .      .   .132        50 183 

14-  •  87        32 133  j    187 

15 87      33 137  |  205 

16. .      .    87      34. .    ..138  j  187 

17. .       .    87      35. .       .138      5  j  205 

18 87      36 171      53 202 

19-  •       -89      37.  .       .171      54 221 

Fort  Wayne  Electric  Co.,  boilers  of,  220. 
Framework    of    Stirling    boiler,     10;    fitting 
brickwork  around,  234,  235. 
Fuel,   adaptation   of   Stirling  boilers   to   dif- 
ferent   kinds    of,    27;    additional    quantity 
needed  for  superheating  steam,   93;  burn- 
ing of,  chapter  141;  calorific  value  of,  105; 
and  chapter  on  determination  of,  131 ;  draft 
required  for  burning,  174,  175. 
Fuels,    bagasse,    121    to    123,    blast   furnace 
gas,  163;  chapter  on,  in;  coals,  in  to  119; 
coal  tar,  129;  coke,  119;  coke  oven  gas,  161; 


244 


THE    STIRLING    WATER-TUBE    SAFETY    BOILER 


corn,  123;  gaseous,  106,  133;  natural  gas, 
128,  129;  patent  or  pressed,  119;  peat,  119; 
petroleum  and  crude  oils,  123  to  127;  spent 
tan,  120;  straw,  120;  water-gas  tar,  129; 
wood,  119,  120;  table  of  tests  of  boilers 
burning  various  kinds  of,  208. 

Fuel  formulas:  Dulong's,  106,  131;  Goutal's, 
136,  137;  Kent's  method,  135,  137;  Hunt's 
for  Illinois  coals,  138;  Mahler's,  132;  cor- 
rection of,  for  hydrogen,  nitrogen,  and 
moisture,  133;  range  of  accuracy  of,  138. 

Furnaces,  design  and  advantages  of  the 
Stirling,  10,  142;  inefficient  forms  of,  142. 

Crases,  course  of  in  the  Stirling  boiler,   n; 

density  of    at    atmospheric   pressure,    182; 

distinction    between    vapors  and,  69;  from 

blast  furnaces,   163;   from  coke  ovens,  161; 

natural,  128,  129;  flue-,  chapter  on  analysis 

of,   181;  molecular    weight  of,  185;  relation 

between  temperature  of  from  furnace,  and 

heating    surface    passed    over,    94;    weight 

and  calorific  value  of,  106,  133. 
Gasoline,    123;  gasoline   test  for  moisture  in 

oil,  124. 
Gauge  glass,  fittings  for,   19;  level  of  water 

in,  203,  231. 

Gauges,    14;    draft,    178;    steam,    231. 
Gauge    pressure    of    steam    as    distinguished 

from  absolute,  72. 
General  Electric  Co.,  boilers  of,  92. 
Globe    valves,    should    always    be    used    for 

feed  valves,   217;  resistance  of    to  flow   of 

steam,   89. 

Goodrich  Co.,  The  B.  F.,  boilers  of,  66. 
Goutal's  fuel  formula,  136,  137. 
Grates,    efficiency    of    in     connection    with 

boiler,   187;  for  bagasse  furnaces,   147;  for 

oil  fuel,  1 50;  for  wood,  147. 
Gravity  of  oils  by  Beaume  hydrometer,  126. 
Grease  in  feed  water,   causes  foaming,   64; 

causes  overheating  of  plates,  64. 
Guanica  Centrale,  boilers  of,  64. 

Hammel  oil  burner,  152. 

Hawaiian  Brewing  &  Malting  Co.,  boilers 
of,  88. 

Head  of  water,  pressure  due  to,  57. 

Heat,  chapter  on,  47;  distribution  of  losses 
of  in  boilers,  191;  effects  of,  47;  latent,  48; 
losses  of  when  burning  anthracite  with  vary- 
ing supply  of  air,  107;  loss  of  in  flue-gases, 
183;  mechanical  equivalent  of,  50;  of  liquid, 


50;  specific,  48,  table,  49;  total,  of  evapora- 
tion or  vaporization,  50;  transfer  of,  50; 
utilization  of  waste,  161. 

Heat  balance,  193,  205. 

Heat  value,  of  bagasse,  121,  122,  123;  of 
blast  furnace  gas,  133,  163;  of  coal,  tables, 
112,  114  to  118,  135;  of  coal  tar,  129;  of 
coke  oven  gas,  161;  of  corn,  123;  of  mis- 
cellaneous gases,  106,  133;  of  natural  gas, 
128,  129;  of  oil  fuel,  124,  125,  127;  of  spent 
tan,  120;  of  straw,  120;  of  water-gas  tar, 
129;  of  wood,  119,  120. 

Heat  value,  formulas  for,  see  fuel  formulas. 

Heaters  for  feed  water,  open,  closed,  and 
economizers,  67. 

Heating  of  feed  water,  chapter  on,  67. 

Heating  furnaces,  utilization  of  waste  heat 
from,  and  tests  of  boilers  installed  in  con- 
nection with,  73. 

Heating  surface,  all  accessible  in  the  Stirling 
boiler,  21;  cleaning  fire  side  of,  228;  effect 
of  soot  in  diminishing  efficiency  of,  23, 
foot-note;  laws  governing  ratio  of,  to  super- 
heating surface  in  boilers,  95  to  99;  rela- 
tion between,  and  the  gas  temperature  and 
amount  of  steam  generated,  94. 

Hoisting  engines,  selecting  boilers  for,  211, 
steam  pipes  and  drums  for,  211. 

Horse-power,  chapter  on,  195;  definition  of, 
195;  of  stationary  and  marine  boilers,  195- 
hourly  evaporation  corresponding  to,  198; 
hourly  consumption  of  steam  per  H.  P. 
of  engines,  198;  indicated  H.  P.  per  boiler 
H.  P.,  table,  196,  197. 

Hot-water  heating,  unique  application  of 
the  Stirling  boiler  to,  29. 

Hunt's  formulas  for  heat  value  of  Illinois 
coals,  138. 

Hydraulic  turbine  tube  cleaner,  care  of,  227; 
cutters  for,  226;  description  of,  225;  operat- 
ing of.  225. 

Hydrogen  available  for  combustion,  106; 
calorific  value  of,  106,  133;  correction  for  in 
fuel  formulas,  133  ;  weight  of,  133. 

Illinois  Steel  Co.,  boilers  of,  222. 

Iloilo  Electric  Light  and  Power  Co.,  boilers 

of,   160. 

Imitations  of  the  Stirling  boiler,  33. 
Impure  feed  water,  action  of  in  the  Stirling 

boiler,    19;   effects   of   and    correctives    for, 

65;  how  to  handle,  61. 
Impurities   in   water,   chapter  on,    57;  effect 


INDEX 


245 


of,  59;  solubilities  of,  60;  where  deposited 
in  boilers,  19. 

Independently-fired    superheater,    102,    104. 

Indicated  engine  horse-power  per  boiler 
horse-power,  196,  197. 

Inefficient  furnaces  for  boilers,  142. 

Injectors,  in  connection  with  boiler  under- 
going test,  202. 

Inland  Steel  Co.,  boilers  of,  190. 

I  et,  direction  of  for  oil  burners,  150. 
Joule's  equivalent  of  heat,  50. 

Kenil  worth  Sugar  Estate,  boilers  of,   144. 

Kent,  Wm.,  statement  of  requirements  for 
burning  coal  without  smoke,  10;  table  of 
horse-powers  of  chimneys,  177;  table  of 
heat  values  of  classes  of  coals,  135,  137. 

Kerosene,  123;  use  of  for  softening  scale,  227. 

Kilowatt-hour,  oil  and  coal  per,  table,   127. 

Kindling  point  of  combustibles,  105. 

Kioto  Electric  Light  Co.,  boilers  of,  34. 

Latent  heat,  48,  of  steam,  50,  69,  74. 

Laws  defining  relation  between  boiler  heating 
surface  and  superheating  surface,  99. 

Leaks,  of  air  into  boiler  settings,  232;  of 
steam  and  water  in  boiler  plants,  232. 

Le  Chatelier's  pyrometer,  51,  52. 

Lehigh  Portland  Cement  Co.,  boilers  of,  no. 

Level  of  water  in  gauge  glass,  203,  231. 

Lignites,  analyses  and  heat  value,  118;  dis- 
integration of  by  weathering,  113;  descrip- 
tion of,  112;  behavior  of  in  furnaces,  142. 

Lime  mortar,  235. 

Linear   expansion   of   substances,    table,    51. 

Liquid,  heat  of,  50. 

Los  Angeles  Gas  and  Electric  Co.  boi- 
lers of,  154. 

Los    Angeles- Pacific    R.  R.,  boilers  of,  211. 

Losses,  of  draft  in  stacks,  171;  of  draft  in 
boilers,  flues,  and  furnaces,  175;  of  heat  in 
boilers  and  distribution  of  same,  191;  of 
heat  when  burning  anthracite  with  varying 
air  supply,  107;  of  pressure  in  pipes  con- 
veying steam,  87,  89. 

Low  water  in  boilers,  231. 

Mahler,  calorimeter,  138;  fuel  formula,  132. 
Management  and  care  of  boilers,  chap,  229. 
Manhole  plates  and  arch  bars,  15. 
Marine    boilers,    as    built  by  THE   STIRLING 
COMPANY,  45;  horse-power  of,  195. 


Marsh  gas,  weight  and  heat  value  of,   133. 
Master  Steamfitters  Association  Standard  for 

pipe  flanges,  217. 

McCahan  Sugar  Refinery,  boilers  of,  18. 
Measurements  of  high  temperature,  51. 
Mechanical  equivalent  of  heat,  50. 
Mechanical  stokers,  145. 
Megass,  see  bagasse. 
Melting  points  of  metals,  51,  52. 
Mercurial  pyrometer,  51. 
Methane,  combustion  data  for,  106. 
Methods  of  firing  coal,  alternate,  coking,  and 

spread- firing,  143. 
Mill  bagasse,  description  and  heat  value  of, 

122,  123. 

Mills  building,  boilers  of,  240. 
Mining  service,  boilers  for,  209. 
Molecular  weight  of  gases,  185. 
Monongahela  Light  and   Power  Co.,  boilers 

of,  86. 
Moisture,  in  bagasse,   147;  correction  for  in 

fuel    formulas,    133;    determination    of    in 

coal,  204. 

Mortar,  for  boiler  settings,  235. 
Mud  in  feed  water,  effect  of,  59. 
Mud    drum,    action    of   in    precipitating   im- 
purities,   19;    door    in    wall    opposite,    23; 

should    be    blown    off    on    outside    before 

emptying  boiler,  231. 

Napier's  formula  for  flow  of  steam  into 
atmosphere,  91. 

Natural  gas,  129;  analyses  and  heat  values, 
128;  arrangement  of  boiler  for  burning,  151 ; 
burning  of,  155;  comparison  of,  with  coal, 
129;  computation  of  heat  value  of,  133; 
test  of  boiler  burning,  157. 

Nipple  for  drawing  off  sample  of  steam  for 
calorimeters,  85. 

Nitrogen,  atomic  weight  of,  105;  corrections 
for  in  fuel  formulas,  133;  dilutes  furnace 
gases  and  causes  heat  loss,  105;  molecular 
weight  of,  185;  weight  and  volume  of,  182. 

Northern  Texas  Traction  Co.,  boilers  of,  156. 

Nova  Scotia  Steel  and  Coal  Co.,  boilers  of,  180. 

Nozzles  for  Stirling  boilers,  115. 

Old  Dominion  Copper  Mining  and  Smelt' 
ing  Co.,  boilers  of,  210. 

Olefiant  gas,  weight  and  heat  value  of,  133, 

Oil,    advantages    and    disadvantages    of,    as 

fuel,   126;  burners  for,   152;  comparison  of, 

with  coal,  126,  127;  composition  and  heat 


246 


THE   STIRLING    WATER-TUBE    SAFETY    BOILER 


values  of,  124,  125;  effect  of  in  boilers  and 
methods  of  removing  from,  228,  2<;i; 

\J 

efficiencies  obtainable  from,  153;  flash  point 
of,  125;  gravity  of  by  Beaume  hydrometer, 
126;  stacks  for  boilers  burning,  178. 

Orsat  apparatus  for  flue-gas   analysis,    184. 

Ost's  theory  of  corrosion  of  boiler  plate  by 
decomposition  of  water,  61, 

Oxygen,  atomic  weight  and  physical  prop- 
erties, 105;  computation  of  weight  of  for 
combustion  of  fuel,  106;  determination  of 
percentage  of  in  flue-gases  by  Orsat  ap- 
paratus, 182. 

Parr's  fuel  calorimeter,  138. 

Peat,  119. 

Peoples  Railway  Company,  boilers  of,  32. 

Petroleum,  see  oil. 

Philadelphia  Museum's  Exposition,  boilers 
of,  134- 

Philadelphia  and  Reading  R,  R.,  boilers  of,  28. 

Pioneer  Iron  Co.,  boilers  of,  168. 

Pipes,  covering  of  for  steam,  219;  flow  of 
steam  through,  87,  89;  flanges  for,  table, 
217;  for  supplying  steam  to  hoisting  en- 
gines, 21 1 ;  table  of  sizes  for  steam,  gas, 
and  water,  213. 

Piping  for  steam,  chapter  on  principles  of, 
213;  diagrams  illustrating  systems  of,  214; 
drainage  of,  214;  duplicate  systems  of, 
216;  location  of  valves  in ,  217. 

Pitting  of  boilers,  61,232. 

Plain  cylinder  boilers,  waste  heat  from,  167. 

Power,  definition,  195 ;  see  horse-power. 

Pressed  fuels,  119. 

Pressure,  due  to  head  of  water,  57;  to  height 
of  chimney,  169;  of  oil  fed  to  burners,  153. 

Priming  in  boilers,  causes  and  remedies,  65, 
231;  due  to  carbonates,  60;  due  to  feeding 
cold  water,  68;  due  to  grease,  64;  due  to 
scum,  60. 

Principles  of  steam  piping,  213. 

Properties  of  saturated  steam,  74. 

Proximate  analysis,  definition,  135;  table 
of  for  coal,  114. 

Purification  of  feed  water  by  chemicals,  61. 

Pyrogallol,  for  Orsat  apparatus,  184. 

Pyrometer,  51;  expansion,  and  errors  of, 
52;  Le  Chatelier's  thermo-electric,  52;  mer- 
curial, 51. 

Quality  of   steam,    204;   definition,   69,    79; 
determination  of,  79  to  85. 


Quick  closing  gauge  glass  fittings,  19. 
Quick  steaming,  comparison  of  various  types 
of  boilers  with  respect  to  capacity  for,  37. 

rvadiation  of  heat,  50;  from  steam  pipes, 
213,  214,  219. 

Rapid  circulation  of  water  in  the  Stirling 
boiler,  13 ;  advantage  of,  15. 

Rate  of  driving,  and  effect  on  boiler  effic- 
iency, 193. 

Ratio  of  air  supplied  to  theoretical  amount, 
for  various  analyses  of  flue-gases,  183,  184. 

Red  brick,  how  they  should  be  laid,  233; 
fitting  of  around  boiler  framework,  234,  235. 

Refractory  scale,  methods  of  softening,  227. 

Removal  of  water  from  steam  mains,   214. 

Repairs,  comparison  of  for  different  types 
of  boiler  at  World's  Columbian  Exposition, 
33 ;  comparison  of  on  Stirling  and  shell  types 
of  boiler,  41  facility  for  making,  to  Stirling 
boiler,  25. 

Report  of  boiler  trials,  forms  for,  206. 

Republic  Iron  and  Steel  Co.,  boilers  at,  130. 

Resistance  of  elbows  and  globe  valves  to 
flow  of  steam,  89. 

Return  tubular  boilers,  explosion  of,  36,  37. 

Riverside  Iron  Works,  boilers  of,  84. 

Robinson's  Central  Deep,  boilers  of,  109. 

Rules  for  conducting  boiler  trials,  201. 

Ruppert  Ice  Co.,  boilers  of,  82. 

Rupture  of  boiler  tubes,  causes  of,  25. 

Safety,  of  the  Stirling  boiler,  17;  of  different 
types  of  boiler  compared,  35. 

Safety  valves,  care  of,  231. 

Saturated  mixtures  of  air  and  vapor,  56. 

Saturated  steam,  table  of  properties  of,    74. 

Saving,  by  covering  steam  pipes,  221;  by 
heating  feed  water,  67. 

Scale,  action  of  Stirling  boiler  in  preventing 
formation  of,  on  hottest  tubes,  19;  diffi- 
culty of  removing  from  fire-tube  boilers 
39;  forms  on  hottest  tubes  of  horizontal 
water-tube  boilers,  21;  how  to  soften  re- 
fractory, 227;  materials  which  form,  59, 
60;  removal  of,  63,  223  to  228. 

Scotch  marine  boilers,  straining  of  due  to 
unequal  expansion,  37 ;  tube  renewals  in,  39. 

Scum,  causes,  effects,  and  method  of  hand- 
ling, 60,  61. 

Sea  water,  boiling  point  and  specific  gravity 
of,  58- 

Selby  Smelting  and  Lead  Works,  boilers  of,  6. 


INDEX 


247 


Settings  for  boilers,  causes  of  cracking  of, 
229;  how  to  dry  them  out,  229;  specifica- 
tions of,  233. 

Sherry  building,  boilers  of,  30. 

Shops  of  THE  STIRLING  COMPANY,  45;  views 
from,  44,  46,  62,  and  frontispiece. 

Simplicity  of  the  Stirling  boiler,  13. 

Smoke,  how  to  burn  coal  without,  10;  elimi- 
nation of  by  using  mechanical  stokers,  145. 

Softening  refractory  scale,  227. 

Solids,  amount  deposited  in  boilers,  59; 
coefficients  of  linear  expansion  of,  51; 
specific  heat  of,  49,  53. 

Solvent  power  of  water,  57. 

Soot,  effect  of  in  reducing  boiler  efficiency,  23. 

Space,  comparison  of  that  needed  for  various 
types  of  boiler,  43 ;  required  by  Stirling 
boiler,  29. 

Spacing  of  tubes  in  Stirling  boilers,  25. 

Specific  heat,  definition,  48;  mean,  for  cer- 
tain solids,  53;  of  air,  53;  table  of  for  solids, 
liquids  and  gases,  49. 

Specific  gravity,  of  fuel  oils,  124,  125;  of 
gases,  182;  of  sea  water,  58. 

Specific  volume  of  steam,  69. 

Stacks,  see  chimneys. 

Standing  unused,  preparing  boilers  for,  232. 

Steam,  absolute  and  gauge  pressure  of,  72; 
chapter  on,  69;  dry,  69,  and  production  of 
by  the  Stirling  boiler,  27;  consumption  of 
by  different  types  of  engine,  198;  economy 
of  high  pressure,  73;  flow  of  into  the  atmos- 
phere, 90,  91;  flow  of  through  pipes,  87,  89; 
latent  heat  of,  50,  69;  per  cent,  of  used  by 
oil  burners,  153;  principles  of  piping  for, 
213;  properties  of  saturated,  tables,  71, 
72,  74  to  77;  quality  of,  69,  79,  204;  re- 
lation between  amount  of  generated,  heating 
surface  passed  over,  and  temperature  of  hot 
gases,  94;  relative  volume  of,  69;  saturated, 
69;  specific  volume  of,  69;  superheated,  69, 
93;  total  heat  of,  69,  74. 

Steam  engine,  efficiency  of  ideal  perfect,  73; 
indicated  horse-power  of  per  boiler  horse- 
power, 196,  197;  steam  consumption  per 
hour  of,  198. 

Steam  gauges,  care  of,  231. 

Steam  main,  cutting  boilers  into,  229;  drain- 
age of,  214. 

Steam  nozzle  pads,  15. 

Steam   pockets   in     water- tube    boilers,    15. 

Steel  framework  of  the  Stirling  boiler,  10; 
fitting  brickwork  around,  235. 


Stirling  bagasse  conveyor  and  automatic 
furnace  feeder,  148, 

Stirling  water- tube  safety  boiler;  adapta- 
tion of  to  different  kinds  of  fuel,  27;  ad- 
vantages of  in  installations  for  saving  waste 
heat,  161  to  167  ;  arch  bars  over  manholes  of, 
15;  baffles  and  course  of  gases  in,  n;  brick 
setting  of,  10,  233;  cleaning  doors  of,  u; 
cleaning  exterior  of,  23,  228;  cleaning  in- 
terior of,  21,  223;  colored  sections  illustrat- 
ing general  design  and  setting  of,  8,  9; 
constriction  of  circulation  obviated  in,  15; 
counterbalanced  fire  doors  of,  31 ;  discussion 
of  efficiency  of,  29 ;  door  and  frame  in  setting 
opposite  mud  drum  of,  23;  driving  at  high 
and  low  rates  of  evaporation,  27;  drum 
lugs  of  wrought  steel,  15;  durability  of,  23; 
early  types  of,  7 ;  elimination  of  tempera- 
ture stresses  from,  37;  facility  of  making 
repairs  to,  25;  forged  steel  drum  heads  of, 
9,  13;  furnace  of,  and  its  advantages,  10, 
142;  imitations  of,  33;  manner  in  which  it 
precipitates  impurities  into  the  mud  drum, 
19;  produces  dry  steam,  27;  provision  for 
expansion  and  contraction  in,  13;  quick 
closing  gauge  glass  fittings  of,  19;  rapid 
circulation  of  water  in,  13;  repairs  of,  in 
comparison  with  those  of  other  types  at 
World's  Columbian  Exposition,  33;  setting 
of,  8,  9;  see  setting;  setting  for  burning  ba- 
gasse, 146,  147;  setting  for  burning  blast 
furnace  gas,  164;  setting  for  burning  coke 
oven  gas,  162;  setting  for  burning  oil  or 
natural  gas,  151;  simplicity  of  design  of, 
13;  steel  firing  and  ash-pit  doors  of,  17; 
space  occupied  by,  29;  steam  nozzle  pads 
of,  15;  steam  space  in,  25;  tests  of,  table, 
208,  see  tests;  tubes  of,  9;  tube  spacing  in, 
25;  unique  use  of,  for  hot-water  heating, 
29;  water  columns  and  connections,  19; 
water  spaces  in,  25.  See  superheater. 

Stirling  chain  grate  stokers,  158,  159. 

STIRLING  COMPANY,  THE,  works  of,  45,  and 
frontispiece. 

Stokers,  mechanical,  145;  chain  grates,  159. 

Stoking  apparatus  for  bagasse,  148. 

Stop  valves  for  boilers,  217. 

Sulphur,  combustion  data  for,  106;  is  des- 
structive  to  boiler  plate,  105. 

Superheater,  chapter  on  the  Stirling,  93; 
course  of  steam  in,  102,  103;  flooding  pipes 
for,  102,  103;  for  boilers  already  installed, 
104;  in  middle  pass  of  boiler,  101;  in  rear 


248 


THE    STIRLING   WATER-TUBE    SAFETY   BOILER 


pass,    100 ;   independently   fired,    102,    104; 

replacing  tubes  of,  103. 
Superheated  steam,   additional  heat  needed 

for    producing,    93;    definition    of,    69,    93; 

specific  heat  of,  93. 
Superheating    surface,    relation    between    it 

and  boiler  heating  surface,  95  to  99. 

1  ables  in  this  book: 

No.        PAGE      No.         PAGE     No.         PAGE 


I 

•  •  33 

22 

.  .  .  91 

43-  • 

.  .  .125 

2 

•  •  47 

23-  • 

•  •  •  93 

44-  • 

.  .  .  126 

3-  •• 

•  •  49 

24.  . 

•••97 

45-  • 

.  .  .127 

4-  • 

..  49 

2S.  ... 

.  .105 

46... 

.  .128 

5--  • 

••  50 

26.  ., 

.  .  106 

47-  • 

•  -133 

6.  .. 

•  •  51 

27.  . 

.  .107 

48.. 

•  -135 

7-  •• 

••  52 

28.  . 

.  .107 

49-  • 

•  -135 

8.  .  . 

•  •  53 

29.  .. 

.  .108 

50... 

.  .  167 

9.  .  . 

••  55 

30.  .. 

in 

51.  .. 

.  .  169 

10 

•  •  56 

31.  .. 

.  .  in 

52.  .  . 

•  -177 

ii 

•  •  57 

32.  .  . 

.  .  112 

53-  •• 

•  -177 

12  .  .  . 

•  •  58 

33-  •  • 

.114 

54-  • 

.  .182 

13.  .. 

.  .  60 

34-  •  • 

.  .119 

55--- 

.  .184 

14.  .  . 

..  6s 

35-  •• 

.  .  I2O 

56... 

.  .186 

15.  .  . 

•  •  71 

36... 

.  .  120 

57-  •  • 

.  .  196 

16.  .  . 

•  •  70 

37-  •• 

.  .  121 

58... 

.  .198 

17.  .. 

•  •  72 

38... 

.  .  122 

59-  •• 

.  .198 

18.  .  . 

•  •  74 

39-  •• 

.  .  122 

60.  .. 

.  .208 

19.  .  . 

.  .  87 

40.  . 

•  -123 

61.  .. 

.213 

20.  .. 

..  8q 

41  .  .  . 

.124 

62.  .. 

.  .  217 

21 

.  .  90 

42.  .. 

..I25 

63... 

.  .  219 

Tar,  analysis  and  heat  value  of,  129. 

Tan,  heat  value  of,  120;  burning  of,  147. 

Temperature,  definition,  47;  of  fire,  50,  and 
method  of  computing,  107 ;  elimination  from 
the  Stirling  boiler  of  stresses  due  to,  37; 
measurement  of  high,  51. 

Tests  of  steam  boilers,  code  of  rules  for,  201 ; 
forms  for  data  and  results  of,  206;  starting 
and  stopping  of,  202. 

Tests  of  Stirling  boilers,  general  table,  208; 
when  burning  green  bagasse,  149;  when 
burning  coke  oven  gas,  163;  when  burning 
blast  furnace  gas,  165 ;  when  burning  natural 
gas,  157;  when  burning  oil,  155;  when  util- 
izing gases  from  heating  furnaces,  167. 

Texas    oils,   125. 

Thermal  unit,  British,  48;  metric,  48. 

Thermometers,  47. 

Throttling  calorimeter,   79  to  85. 

Tiles  for  Stirling  boiler  baffles,  n;  laying  of, 
237,  not  destroyed  by  tubes  passing  between 
them,  ii. 


Time  required  for  cleaning  boilers,  31. 

Transfer  of  heat,  50. 

Trials  of  boilers,  code  of  rules  for,  201. 

Turbine   tube  cleaner,    223. 

Tubes,  causes  of  rupture  of,  25;  description 
of  those  used  in  the  Stirling  boiler,  9 ;  great 
advantage  of  curved,  13;  method  of  ascer- 
taining whether  there  is  any  deposit  in ,  21; 
renewals  of  in  Scotch  marine  boilers,  39; 
spacing  of  and  ease  of  replacing  them  in  the 
Stirling  boiler,  25;  unfounded  objection  to 
curved,  21. 

Union  Steel  Co.,  boilers  of,  54,  200. 
Unit  of  evaporation,  72,  207,  foot-note. 
Utilization  of  waste  heat,  161. 
U-tube  draft  gauge,  179. 

Vacuum,  gauges  for  indicating,  72;  prop- 
erties of  steam  for  various  amounts  of,  71. 

Valves,  blow-off,  231 ;  care  of  safety,  231 ;  on 
boilers,  217  ;  location  of  in  steam  mains,  217. 

Vapor,  as  distinguished  from  a  gas,  69; 
amount  of  in  air,  55,  56. 

Volatile  matter  in  fuel,  a  cause  of  smoke 
and  low  boiler  efficiency,  141 ;  contains  con- 
stituents which  are  not  really  combustible, 
112,  foot-note;  requirements  for  burning 
of,  10 ;  how  the  Stirling  furnace  meets  these 
requirements,  142. 

Warren  hydrocarbon  burner,  152. 

Waste  heat,  chapter  on  utilization  of,  16 1. 

Water,  chapter  on,  57;  boiling  point  at  dif- 
ferent altitudes,  58;  hourly  evaporation  of 
per  boiler  horse-power,  198;  removal  of 
from  steam  pipes,  214;  see  feed  water. 

Water  column  of  Stirling  boilers,  19. 

Water  space  in  Stirling  boilers,  25,  43. 

Water-tube  versus  fire-tube  boilers,  35. 

Water-gas  tar,  129. 

Weathering  of  coal,  113. 

Weights,  combining,  of  chemical  elements, 
1 05;  molecular,  of  gases,  185. 

Whitman    and    Barnes    Co.,  boilers  of,  42. 

Wolverine  Mining  Co.,  boilers  of,  238. 

Wood,  composition  of,  119,  120;  heat  values 
of,  120;  methods  of  burning,  145. 

Works  of  THE  STIRLING  COMPANY,  45; 
views  of,  44,  46,  62,  and  frontispiece. 

World's  Columbian  Exposition,  table  show- 
ing causes  of  withdrawal  from  service  of 
water-tube  boiler  operating  at,  33. 


